Peripheral Nerve Field Stimulation Control

ABSTRACT

Peripheral nerve field stimulation (PNFS) may be controlled based on detected physiological effects of the PNFS, which may be an efferent response to the PNFS. In some examples, a closed-loop therapy system may include a sensing module that senses a physiological parameter of the patient, which may be indicative of the patient&#39;s response to the PNFS. Based on a signal generated by the sensing module, the PNFS may be activated, deactivated or modified. Example physiological parameters of the patient include heart rate, respiratory rate, electrodermal activity, muscle activity, blood flow rate, sweat gland activity, pilomotor reflex, or thermal activity of the patient&#39;s body. In some examples, a patient pain state may be detected based on a signal generated by the sensing module, and therapy may be controlled based on the detection of the pain state.

This application claims the benefit of U.S. Provisional Application No.61/051,955 to King et al., entitled, “PERIPHERAL NERVE FIELD STIMULATIONCONTROL” and filed on May 9, 2008. The entire content of U.S.Provisional Application No. 61/051,955 is incorporated herein byreference.

TECHNICAL FIELD

The disclosure relates to medical devices, and, more particularly, tocontrol of therapy delivery by medical devices.

BACKGROUND

A variety of therapies, such as neurostimulation or therapeutic agents,e.g., drugs, may be delivered to a patient to treat chronic or episodicpain. Examples of neurostimulation therapies used to treat pain aretranscutaneous electrical nerve stimulation (TENS), percutaneouselectrical nerve stimulation (PENS), peripheral nerve stimulation (PNS),spinal cord stimulation (SCS), deep brain stimulation (DBS), andcortical stimulation (CS). Examples of drugs used to treat pain areopioids, cannabinoids, local anesthetics, baclofen, adenosine andalpha-blockers.

PNS, SCS, DBS and CS are typically delivered by an implantable medicaldevice (IMD). An IMD delivers electrical stimulation therapy viaelectrodes, which are typically coupled to the IMD by one or more leads.The number and positions of the leads and electrodes is largelydependent on the type or cause of the pain, and the type ofneurostimulation delivered to treat the pain. In general, an IMDdelivers neurostimulation therapy in the form of electrical pulses.

SCS involves stimulating the spinal cord at specifically targetedlocations, typically via leads and electrodes that are either surgicallyimplanted post laminectomy, or inserted percutaneously in the epiduralspace. Delivering stimulation to the appropriate location on the spinalcord causes paresthesia that overlays the pain region to reduceperception of pain. SCS can result in the patient experiencingparesthesia in a relatively large area, including more than one limb. Insome cases, SCS may be effective for neuropathic pain, such asneuropathy or radiculopathy that involves a significant portion of onelimb and more than one dermatome.

PNS is typically used to treat patients suffering from intractable painassociated with a single nerve. PNS places a group of electrodes in veryclose proximity to, e.g., in contact with, and approximately parallel toa major nerve in the subcutaneous tissue. PNS may also place a group ofelectrodes in very close proximity to a nerve that may be deeper in thelimb. Placing electrodes in very close proximity to the nerve may ensurethat only fibers within that nerve are activated at low amplitudes.

PNS electrodes may be located on percutaneous leads, but for stabilityand to prevent stimulation of other tissues proximate to the targetperipheral nerve, PNS electrodes are generally located within insulativematerial that wraps around a nerve, e.g., cuff electrodes, or on onesurface of a flat paddle of insulative material placed under a nerve. Inany case, the electrodes for PNS are placed in close proximity to thenerve “upstream” from the source of damage or pain, e.g., closer to thespinal cord than the region of damage or pain. When electrodes areimplanted upstream, the paresthesia resulting from PNS may extend to abroader area innervated by the target peripheral nerve. Examples ofupper extremity nerves that may be treated with PNS include the ulnarnerve, median nerve, radial nerve, tibial nerve and common peronealnerve.

DBS and CS can be used to treat neuropathic and nociceptive pain throughdelivery of stimulation to various structures of the brain. In somecases, DBS may treat pain through delivery of stimulation to gray matterwithin the midbrain, or the thalamus, via electrodes implanted in thebrain. CS may treat pain through delivery of stimulation to the sensoryand/or motor cortex via electrodes placed in or on the cortex.

Therapeutic agents that treat pain may be delivered by an implantablepump, external pump, transdermally, or orally. Typically, an implantablepump delivers one or more therapeutic agents to a target location via acatheter. The target location may be intrathecal or extradural.

SUMMARY

In general, the disclosure describes techniques for controllingstimulation therapy, such as peripheral nerve field stimulation (PNFS),based on detected physiological effects of the therapy on a patient. Insome examples, a desired physiological effect of PNFS may be associatedwith a particular physiological parameter of the patient, and therapymay be delivered to the patient based on the detection of aphysiological parameter characteristic. Example physiological parametersof the patient include heart rate, respiratory rate, electrodermalactivity (e.g., galvanic skin response or skin conductance response),muscle activity (e.g., electromyogram (EMG)), blood flow rate, sweatgland activity, pilomotor reflex (e.g., goose bumps), or thermalactivity of the patient's body. The physiological parametercharacteristic may be, for example, an amplitude, trend, or frequencyband characteristic of a signal that changes as a function of thephysiological parameter (e.g., a “physiological signal”). In otherexamples, the desired physiological parameter characteristic may be acharacteristic of a physiological signal from a control physiologicalsignal. The control physiological signal may indicate the activity ofthe physiological parameter within a region of the patient's body thatis generally unaffected by the delivery of PNFS. For example, thecontrol signal may be indicative of the physiological parameter in aportion of the patient's body outside of the region in which the PNFS isdelivered, which may also be the region in which the patient perceivespain.

In one technique for controlling therapy delivery, therapy may bedelivered until the physiological parameter characteristic is detected.In another example technique, therapy may be delivered to maintain thephysiological parameter characteristic above a threshold, within acertain window of values, or below a threshold.

In some examples, PNFS is delivered to the patient to generate anafferent response, such as to relieve pain. The stimulation therapy mayincidentally activate efferent nerves, thereby resulting in an efferentresponse from the patient, which may generate a detectable change in aphysiological parameter of the patient. The detected physiologicaleffects of the therapy on the patient that is used to control therapymay, therefore, be an efferent response. In this way, the patient'sefferent response to stimulation may be used in a closed-loop therapysystem in order to control the therapy delivery, such as to activate ordeactivate therapy delivery or to titrate the therapy parameter values.

In some examples, a characteristic of a physiological signal may beassociated with a patient pain state. The physiological signal may beindicative of a patient parameter that changes in response to deliveryof PNFS therapy. Detection of the pain state via the characteristic ofthe physiological signal may be used in a closed-loop therapy system tocontrol the delivery of PNFS to the patient. In some examples, a devicemonitors a physiological signal of a patient and determines whether thesignal indicates the patient is in a pain state. The device may controlthe delivery of PNFS to a patient based on the detection of the painstate.

In one example, the disclosure describes a method comprising deliveringperipheral nerve field stimulation to a region of a body of a patient inwhich the patient experiences pain via at least one electrode implantedin the region, receiving a signal indicative of a physiologicalparameter of the patient, wherein the signal indicates a response of thepatient to the peripheral nerve field stimulation, and controlling thedelivery of the peripheral nerve field stimulation based on the signal.

In another example, the disclosure describes a method comprisingdelivering peripheral nerve field stimulation to a region of a body of apatient in which the patient experiences pain via at least one electrodeimplanted in the region, detecting an efferent response of the patientto the delivery of peripheral nerve field stimulation, and controllingthe delivery of the peripheral nerve field stimulation based on thedetected efferent response.

In another example, the disclosure describes a system comprising asensing module that generates a signal indicative of a physiologicalparameter of a patient, a medical device that delivers peripheral nervefield stimulation to a region of a body of the patient in which thepatient experiences pain via at least one electrode implanted in theregion, and a processor that receives the signal from the sensing moduleand controls the delivery of the peripheral nerve field stimulation bythe medical device based on the signal. The signal indicates a responseof the patient to the peripheral nerve field stimulation.

In another example, the disclosure describes a system comprising meansfor delivering peripheral nerve field stimulation to a region of a bodyof a patient in which the patient experiences pain via at least oneelectrode implanted in the region, means for receiving a signalindicative of a physiological parameter of the patient, wherein thesignal indicates a response of the patient to the peripheral nerve fieldstimulation, and means for controlling the delivery of the peripheralnerve field stimulation based on the physiological signal.

In another example, the disclosure describes a method comprisingreceiving a signal indicative of a physiological parameter of a patient,determining a patient pain state based on the signal, and based on thepatient pain state, controlling the delivery of peripheral nerve fieldstimulation to a region of a body of the patient in which the patientexperiences pain via at least one electrode implanted in the region.

In another example, the disclosure describes a system comprising asensing module that generates a signal indicative of a physiologicalparameter of a patient, a medical device that delivers peripheral nervefield stimulation to a region of a body of the patient in which thepatient experiences pain via at least one electrode implanted in theregion, and a processor that receives the signal from the sensingmodule, determines a patient pain state based on the signal, andcontrols the delivery of the peripheral nerve field stimulation based onthe determined pain state.

In another example, the disclosure describes a system comprising meansfor receiving a signal indicative of a physiological parameter of apatient, means for determining a patient pain state based on the signal,and means for controlling delivery of peripheral nerve field stimulationto a region of a body of the patient in which the patient experiencespain based on the patient pain state. The peripheral nerve fieldstimulation is delivered via at least one electrode implanted in theregion.

In another example, the disclosure describes a computer-readable mediumcontaining instructions. The instructions cause a programmable processorto perform any of the techniques described herein.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an example system fordelivering peripheral nerve field stimulation (PNFS) to a patient.

FIGS. 2A and 2B are functional block diagrams illustrating components ofexample implantable medical devices that deliver PNFS to a patient.

FIG. 3 is a functional block diagram illustrating components of anexample clinician programmer.

FIG. 4 is a functional block diagram illustrating components of anexample patient programmer.

FIGS. 5-9 are flow diagrams illustrating example techniques forcontrolling an implantable medical device based on a sensedphysiological parameter of a patient.

FIG. 10 is a flow diagram illustrating an example technique fordetermining a physiological signal characteristic that may be used tocontrol PNFS delivery.

FIG. 11 is a flow diagram illustrating an example technique fordetermining the validity of a patient's modification to a therapyprogram.

FIG. 12 is a flow diagram illustrating an example technique forassociating a patient pain state with a characteristic of aphysiological signal.

FIGS. 13 and 14 are flow diagrams illustrating example techniques forcontrolling delivery of PNFS based on a detected pain state.

FIGS. 15A and 15B are flow diagrams illustrating an example techniquefor modifying PNFS.

FIG. 16 is a conceptual diagram illustrating another example system fordelivering PNFS to a patient.

FIG. 17 is a flow diagram illustrating an example technique forcontrolling an implantable medical device based on a controlphysiological signal.

DETAILED DESCRIPTION

Peripheral nerve field stimulation (PNFS) is electrical stimulationdelivered via one or more implanted electrodes. The electrodes arepositioned, i.e., implanted, in the tissue of a patient within theregion in which the patient experiences pain. The electrodes may beimplanted within, for example, intra-dermal, deep dermal, orsubcutaneous tissues of the patient. The PNFS current may spread alongpaths of lower resistance in any of numerous directions from electrodes,but generally spreads parallel to the skin surface. The PNFS current mayspread over an area of several square centimeters. PNFS is notdeliberately delivered to a specific nerve, but may excite nearbynerves.

Depending on the location at which the electrodes are implanted, PNFSmay be used to treat a variety of types of pain. PNFS may beparticularly effective at treating localized types of pain. For example,PNFS may be used to treat pain associated with failed back surgerysyndrome (FBBS) or other low back pain, cervical pain, such as in theshoulder or neck, neuralgia or other pain associated with occipitalnerves, supra-orbital pain, facial pain, inguinal or other pelvic pain,intercostal or other chest pain, limb pains, phantom limb pain, visceralpain, especially if it is referred to a superficial structure, peronealpain, or arthritis.

FIG. 1 is a conceptual diagram illustrating an example therapy system 10for treating pain of a patient 12 by delivering PNFS to patient 12.System 10 includes an implantable medical device (IMD) 14 that deliversPNFS therapy to patient 12. IMD 14 may include circuitry for thegeneration of electrical stimulation signals, which may be pulses asprimarily described herein, or continuous time signals, such as sinewaves, for delivery to patient 12 via selected combinations ofelectrodes (not shown in FIG. 1) carried by lead 16.

Lead 16 may comprise, for example, a substantially cylindrical lead withring electrodes, a paddle lead, or a lead within a more complex,three-dimensional electrode array geometry, such as a cylindrical leadwith electrodes disposed at various circumferential positions around thecylinder. In some examples, as discussed in greater detail below, thelead may have electrodes, such as pad electrodes, on more than onesurface. For example, lead 16 may be a paddle-type lead with electrodeson multiple surfaces, or a multiple level lead, as described incommonly-assigned U.S. patent application Ser. No. 11/450,133 to Rooneyet al., entitled, “COMBINATION THERAPY INCLUDING PERIPHERAL NERVE FIELDSTIMULATION” and filed on Jun. 9, 2006. U.S. patent application Ser. No.11/450,133 to Rooney et al. is incorporated herein by reference in itsentirety. The devices, systems, and techniques described herein are notlimited to use of any of the leads described herein, or any particulartype of implantable lead.

In addition, in other examples, more than one lead may be coupled to IMD14 to deliver PNFS to patient 12. For example, multiple leads may extendfrom IMD 14 to the same region or different regions of pain withinpatient 12. As an example, each of four leads 16, each with twoelectrodes, may extend to a respective, particular region 18 wherepatient 12 experiences pain. Lead 16 may be bifurcated, particularly ifthe number of interfaces that IMD 14 provides for electrically couplinga stimulation generator within IMD 14 to leads is limited. Although notshown in FIG. 1, lead 16 may be coupled to IMD 14 by one or moreextensions. In some examples, IMD 14 may also include additional leadsso as to deliver one or more other therapies, such as SCS, incombination with PNFS, e.g., as described in U.S. patent applicationSer. No. 11/450,133 to Rooney et al.

Lead 16 delivers PNFS from IMD 14 to the tissue of patient 12 within aregion 18 where patient 12 experiences pain. Lead 16 may be implantedwithin or between, for example, intra-dermal, deep dermal, orsubcutaneous tissue of patient 12 at the region 18 where patient 12experiences pain to deliver PNFS. Subcutaneous tissue includes skin andassociated nerves, and muscles and associated nerves or muscle fibers.In the illustrated example, region 18 is an axial region of the lowerback of patient 12. In other examples, lead 16 may be implanted in anyregion where patient 12 experiences pain. Lead 16 may deliver PNFS toone layer of tissue or multiple layers of a tissue as determinednecessary by a physician.

In general, lead 16 may extend from IMD 14 to any localized area ordermatome in which patient 12 experiences pain. For example, lead 16 mayextend from IMD 14 to position electrodes at various regions of theback, the back of the head, above the eyebrow, and either over the eyeor under the eye, and may be used to treat failed back surgery syndrome(FBBS), cervical pain (e.g., shoulder and neck pain), facial pain,headaches supra-orbital pain, inguinal and pelvic pain, chest andintercostal pain, mixed pain (e.g., nociceptive and neuropathic),visceral pain, neuralgia, peroneal pain, phantom limb pain, andarthritis. Therapy system 10 is useful for managing pain associated withother patient conditions.

PNFS provided by therapy system 10 may ameliorate pain within the regionof implantation by stimulating axons or small nerve fibers in the nearbydermal, subcutaneous, or muscular tissues, or the tissues themselves.The stimulation of these axons or fibers may cause orthodromic actionpotentials that propagate toward spinal cord 19, and modulate largerperipheral nerves and dorsal horn cells and/or synapses within thedermatomes that include the pain region, which may reduce painexperienced by patient 12 in that region. In some cases, patient 12 mayexperience paresthesia in the dermatome where the electrodes of lead 16are placed. However, in other cases, patient 12 may not experienceparesthesia in the dermatome where the electrodes of lead 16 are placed.The stimulation of these axons or fibers may also cause antidromicaction potentials that propagate toward the skin and modulatesympathetic outflow, which may reduce pain mediated by the sympatheticsystem, such as with some forms of complex regional pain syndrome. Lead16 is not implanted proximate to larger, peripheral nerves in order toavoid delivery of stimulation to smaller fibers in the nerve, e.g.,A-delta fibers, which may result in a patient experiencing unpleasantsensations. However, A-delta fibers may be incidentally recruited duringPNFS.

By way of contrast, peripheral nerve stimulation (PNS), involvesdelivery of stimulation to a specific peripheral nerve via one or moreelectrodes implanted proximate to or in contact with a peripheral nerve,e.g., cuff electrodes surrounding the peripheral nerve. PNS may be usedto deliver stimulation to, for example, the vagal nerves, cranialnerves, trigeminal nerves, ulnar nerves, median nerves, radial nerves,tibial nerves, and the common peroneal nerves. When PNS is delivered totreat pain, one or more electrodes are implanted proximate to or incontact with a specific peripheral nerve that is responsible for thepain sensation.

PNS causes orthodromic action potentials to propagate to the spinal cordvia the specific peripheral nerve, diminishing pain. Typically, however,the electrodes are implanted proximate to the peripheral nerve,“upstream” from the region in which a patient perceives the pain, i.e.,closer to the spinal cord than the region of pain. For PNS therapy, itis considered desirable to implant the electrodes upstream from theregion in which a patient perceives pain so that the paresthesiaresulting from PNS is as widely distributed as the areas innervated bythe peripheral nerve, covering one or more complete dermatomes.

PNFS delivery may recruit sensory afferent nerve fibers, therebygenerating an afferent response by patient 12 that results in mitigationof pain. An afferent response may include sensory physiologicalresponses that result from nerve impulses traveling from sensory orreceptor neurons toward the central nervous system. In some cases, it isbelieved that during delivery of PNFS to region 18 where patient 12experiences pain, delivery of PNFS by IMD 14 activates efferent nerves.The recruitment of the efferent nerves may generate an efferent responseby patient 12, which may also be an autonomic response to the PNFS.Efferent responses may include motor responses that result from nerveimpulses traveling from the central nervous system to effectors, such asmuscle, glands, and the like.

Efferent responses to delivery of PNFS may cause a detectablephysiological effect in patient 12, which, in some cases, may be focusedwithin region 18. For example, if PNFS is delivered to region 18 thatincludes muscle, the efferent response may cause muscle contractionswithin region 18 or proximate to region 18. As another example, if PNFSis delivered to region that includes skin or is proximate to the skin(e.g., the epidermis layer), the efferent response may include a changein cutaneous blood flow, a change in sweat gland activity (e.g., causingperspiration) or a pilomotor reflex. Accordingly, detectable efferentresponses from delivery of PNFS to region 18 of patient 12 may result ina physiological effect that may be detected by monitoring aphysiological parameter of patient, such as a heart rate, respiratoryrate, electrodermal activity (e.g., galvanic skin response or skinconductance response), muscle activity (e.g., electromyogram (EMG)),blood flow rate, sweat gland activity, pilomotor reflex, or thermalactivity of the patient's body.

Therapy system 10 includes sensing module 20, which generates a signalthat changes as a function of a physiological parameter of patient 12.Sensing module 20 may include any suitable circuitry for sensing one ormore physiological parameters of patient 12. The signal generated bysensing module 20 may be used to detect a physiological effect from thedelivery of PNFS to patient 12 by IMD 14. The sensed physiologicaleffect may be, but is not necessarily, an efferent response to the PNFS.In some examples, patient 12 is not conscious of the physiologicaleffect because the physiological effect may be a relatively subtlechange in a physiological parameter, such as a subtle change in thepatient's muscle tone or blood flow rate. Accordingly, the PNFS therapymay cause a physiological effect that is below a threshold level forcausing paresthesia, and sensing module 20 may detect the subtlephysiological effect. IMD 14 or another device may control the deliveryof PNFS to maintain the physiological effect that is below the level ofparesthesia.

In some examples, the sensed physiological effect correlates with adesired therapeutic effect. For example, if PNFS provides efficacioustherapy to patient 12 by activating muscle afferents, then changes tomuscle activity of the patient 12 within region 18 may correlate well tothe desired therapeutic effect. In some examples, the sensedphysiological effect is coincidental to other mechanisms that relievethe patient's pain. For example, if PNFS provides efficacious therapy topatient 12 by activating sufficient numbers of A-beta fibers, thenchanges to the patient's skin, such as the skin conductance, blood flowrate or pilomotor reflex, may be coincidental to the PNFS therapy. Asanother example, if PNFS provides efficacious therapy to patient 12 byactivating A-gamma fibers, then changes to the patient's muscle activitymay be coincidental to the PNFS therapy. As another example, if PNFSincidentally recruits a sufficient number of A-delta or C-fibers, thenthe patient's thermal activity, e.g., body temperature or local tissuetemperature, may be coincidental to the PNFS therapy.

As described in further detail below with reference to FIGS. 5-9, thephysiological signal generated by sensing module 20 may be useful forcontrolling the delivery of PNFS by IMD 14, e.g., in a closed-looptherapy system, such as to activate or deactivate therapy or modify atherapy program. For example, IMD 14 may deliver therapy to patient 12to maintain a certain physiological effect, which may be associated witha characteristic of the physiological signal, such as an amplitude ofthe physiological signal waveform, a trend in the physiological signalwaveform, a power level of the physiological signal measured in aparticular frequency band of the physiological signal waveform, ratiosof power levels between different frequency bands, and the like.

As another example, IMD 14 may deliver therapy to patient 12 to maintaina certain physiological effect that is generally indicated by a controlsignal generated by a second, control sensing module (shown in FIG. 16)that senses one or more physiological parameters of patient 12. Manyphysiological effects from the delivery of PNFS may be relatively localin nature. For example, delivery of PNFS to region 18 may result in achange skin temperature proximate to region 18, a perspiration on a skinsurface (e.g., the epidermis) within region 18, muscle activity (e.g.,detectable by EMG) within region 18, and the like. Accordingly, asdescribed with respect to FIGS. 16 and 17, in some examples, thephysiological signal generated by sensing module 20 may be compared to asecond physiological signal (e.g., a “control” physiological signal) inorder to control the delivery of PNFS by IMD 14. The control signal mayindicate the activity of the physiological parameter in a region of thepatient's body that is generally does not indicate the physiologicaleffects of the PNFS. For example, the control physiological signal maybe indicative of the physiological parameter of patient in an area ofthe patient's body outside of region 18,

In some examples, the control physiological signal is generated by acontrol sensing module that is separate from sensing module 20 andmeasures the same physiological parameter as sensing module 20. In otherexamples, the control physiological signal is generated by sensingmodule 20 or sensing module within IMD 14. As an example of the use of acontrol physiological signal, if therapy system 10 is implemented tominimize back spasms of patient 12, sensing module 20 may measure EMGwithin region 18. A second, control sensing module, as shown in FIG. 16,monitors an EMG of another region of the patient's body that does nothave back spasms. A controller (e.g., a processor within IMD 14) maycontrol IMD 14 to deliver PNFS until the physiological signal fromsensing module 20 substantially matches the signal from the controlsensing module.

The physiological parameter that sensing module 20 monitors may beselected based on the physiological effects of PNFS on patient 12, andmay include, for example, at least one of a heart rate, respiratoryrate, electro-dermal activity, muscle activity (e.g., EMG), blood flowactivity, sweat gland activity, reflex responses (e.g., pilomotor reflexresponses), skin conductance, or thermal activity of the patient's body.Physiological effects from PNFS may be detected by sensing other patientparameters. As described in further detail below, during a learningstage, a physiological signal characteristic may be associated with aknown physiological effect.

Sensing module 20 may be external to patient 12 or may be implantedwithin patient 12. In addition, sensing module 20 may be coupled to IMD14 or may be physically separate from IMD 14, as conceptually shown inFIG. 1. Thus, in some examples, sensing module 20 is incorporated withina common outer housing with the stimulation generator of IMD 14 orattached to an outer housing of IMD 14. When sensing module 20 is in aseparate housing than IMD 14, sensing module 20 may be implanted withinregion 18, proximate to region 18, or distanced from region, dependingon the physiological effect that is detected with the aid of sensingmodule 20. For example, to detect muscle activity within region 18,sensing module 20 may be implanted within region 18 or external topatient 12 proximate to region 18. Sensing module 20 may communicatewith IMD 14 via a wired connection or via wireless communicationtechniques. In some examples, therapy system 10 may include senseelectrodes positioned on lead 16 or one or more separate leads that arecoupled to IMD 14, or electrodes on a housing of IMD 14, which may beused in addition to or instead of sensing module 20. Accordingly, whiletherapy system 10 including a separate sensing module 20 is primarilyreferred to herein, in other examples, therapy systems may include senseelectrodes coupled to IMD 14.

Efficacious PNFS may have an underlying effect on muscle tissue withinor proximate to region 18. In some examples, sensing module 20 or senseelectrodes on lead 16 or one or more separate leads detect theelectrical potential generated by the patient's muscle in region 18.That is, in some examples, sensing module 20 includes one or moreelectrodes positioned to detect EMG signals, which may indicate changesto the patient's muscle tone (e.g., muscle contraction or relaxation) inresponse to PNFS. The changes in the muscle tone may not be noticeableto patient 12. Muscle tone may be sensed using any suitable type ofsensor.

In addition to or instead of EMG sensing electrodes, sensing module 20may include one or more thermal sensing electrodes positioned on thepatient's skin in order to detect sweat gland activity or electrodespositioned on the patient's skin to detect an increased blood flow orpilomotor reflex responses. The increased blood flow within region 18may also be detected by sensors positioned on leads 16, such as a laserDoppler sensor that detects blood cell velocity or an opticaltransmissivity measuring device that detects blood flow. In addition toor instead of the EMG or thermal sensing electrodes, sensing module 20may include a respiration belt, an electrocardiogram (ECG) belt,implanted electrodes that measure ECG, or components that measuretransthoracic impedance, which may be indicative of respiration.

System 10 also includes a clinician programmer 22. Clinician programmer22 may, as shown in FIG. 1, be a handheld computing device. Clinicianprogrammer 22 includes a display 24, such as a liquid crystal display(LCD) or light emitting diode (LED) display, to display informationrelating to PNFS and one or more of the other therapies to a user.Clinician programmer 22 may also include a keypad 26, which may be usedby a user to interact with clinician programmer 22. In some examples,display 24 may be a touch screen display, and a user may interact withclinician programmer 22 via display 24. A user may also interact withclinician programmer 22 using peripheral pointing devices, such as astylus or mouse. Keypad 26 may take the form of an alphanumeric keypador a reduced set of keys associated with particular functions.

A clinician or physician (not shown) may use clinician programmer 22 toprogram PNFS for patient 12. In particular, the clinician may useclinician programmer 22 to select values for therapy parameters, such aspulse amplitude, pulse width, pulse rate, electrode polarity and dutycycle. IMD 14 may deliver the PNFS according to a therapy program thatdefines values for each of a plurality of such therapy parameters. Insome examples, varying the pulse frequency may allow PNFS to capturetarget nerve fibers, such as small, medium, or large fibers sensitive topulse frequency.

Further, IMD 14 may deliver PNFS in combination with other therapy inaccordance with a program group. A program group may contain one or moreprograms. A program group may include one or more PNFS programs and oneor more programs for the other therapy. IMD 14 may deliver stimulationpulses according to a program group by “interleaving” the pulses foreach program, e.g., delivering each successive pulse according to adifferent one of the programs of the program group. To create programsand program groups the clinician may select existing or predefinedprograms, or specify programs by selecting therapy parameter values. Theclinician may test the selected or specified programs on patient 12, andreceive feedback from patient 12. Highly rated programs (e.g.,relatively efficacious programs) may be provided to IMD 14 or a patientprogrammer, individually or as program groups, and used by IMD 14 tocontrol delivery of stimulation. The clinician may identify preferredprograms for PNFS and one or more other therapies separately or throughdelivery of the therapies together.

System 10 also includes a patient programmer 28, which also may, asshown in FIG. 1, be a handheld computing device. Patient programmer 28may also include a display 30 and a keypad 32, to allow patient 12 tointeract with patient programmer 28. In some examples, display 30includes a touch screen display, and patient 12 interacts with patientprogrammer 28 via display 30. Patient 12 may also interact with patientprogrammer 28 using peripheral pointing devices, such as a stylus ormouse.

Patient 12 may use patient programmer 28 to control the delivery of PNFSby IMD 14. For example, patient 12 may use patient programmer 28 toactivate or deactivate PNFS, and to select the programs or program groupthat will be used by IMD 14 to deliver PNFS. Further, patient 12 may usepatient programmer 28 to make adjustments to programs or program groups.For example, upon determining that the current therapy program isineffective at mitigating pain, patient 12 may increase the current orvoltage amplitude of PNFS in order to increase the intensity of thestimulation. Patient programmer 28 may be useful, therefore, forcontrolling the PNFS therapy based on the patient's needs. The patient'sneeds may change, e.g., depending on the time of day or the currentactivity undertaken by patient. Additionally, the clinician or patient12 may use programmers 22, 28 to create or adjust schedules for deliveryof PNFS. As described in further detail below, in some examples, patient12 may use patient programmer 28 or another device in order to setacceptable ranges or thresholds for certain physiological parametervalues that are used in the control of IMD 14.

IMD 14, clinician programmer 22, patient programmer 28, and sensingmodule 20 may, as shown in FIG. 1, communicate via wirelesscommunication. Clinician programmer 22 and patient programmer 28 may,for example, communicate via wireless communication with IMD 14 usingany telemetry techniques known in the art. Such techniques may includelow frequency or radiofrequency (RF) telemetry, but other techniques arealso contemplated. Clinician programmer 22 and patient programmer 28 maycommunicate with each other using any of a variety of local wirelesscommunication techniques, such as RF communication according to the802.11 or Bluetooth specification sets, infrared communication accordingto the IrDA specification set, or other standard or proprietarytelemetry protocols.

Clinician programmer 22 and patient programmer 28 may, but need notcommunicate wirelessly. For example, programmers 22 and 28 maycommunicate via a wired connection, such as via a serial communicationcable, or via exchange of removable media, such as magnetic or opticaldisks, or memory cards or sticks. Further, clinician programmer 22 maycommunicate with one or both of IMD 14 and patient programmer 28 viaremote telemetry techniques known in the art, communicating via a localarea network (LAN), wide area network (WAN), public switched telephonenetwork (PSTN), or cellular telephone network, for example.

FIG. 2A is a functional block diagram illustrating components of anexample of IMD 14 in greater detail. IMD 14 is coupled to lead 16, whichinclude electrodes 40A-40D (collectively “electrodes 40”). Although IMD14 is coupled directly to leads 16 in FIG. 2A, in other examples, IMD 14may be coupled to lead 16 indirectly, e.g., via a lead extension. IMD 14includes therapy module 42, processor 44, memory 46, power source 48,and telemetry module 50.

IMD 14 may deliver electrical stimulation therapy to patient 12 viaelectrodes 40 of lead 16. In the example shown in FIG. 2A, implantablemedical lead 16 is substantially cylindrical, such that electrodes 40are positioned on a rounded outer surface of lead 16. As previouslydescribed, in other examples, lead 16 may be, at least in part,paddle-shaped (i.e., a “paddle” lead). In some examples, electrodes 40may be ring electrodes. In other examples, electrodes 40 may besegmented or partial ring electrodes, each of which extends along an arcless than 360 degrees (e.g., 30-120 degrees) around the outer perimeterof lead 16. The use of segmented or partial ring electrodes may alsoreduce the overall power delivered to electrodes 40 by IMD 14 because ofthe ability to more efficiently deliver stimulation to a targetstimulation site by eliminating or minimizing the delivery ofstimulation to unwanted or unnecessary regions within patient 12.

The configuration, type, and number of electrodes 40 illustrated in FIG.2A are merely exemplary. For example, in other examples, IMD 14 may becoupled to one lead with eight electrodes on the lead or three or moreleads with the aid of bifurcated lead extensions. Electrodes 40 areelectrically coupled to a therapy module 42 of IMD 14 via conductorswithin lead 16. Each of the electrodes 40 may be coupled to separateconductors so that electrodes 40 may be individually selected, or insome examples, two or more electrodes 40 may be coupled to a commonconductor. In one example, an implantable signal generator or otherstimulation circuitry within therapy module 42 delivers electricalsignals (e.g., pulses or substantially continuous-time signals, such assinusoidal signals) to a target tissue site 18 within patient 12 via atleast some of electrodes 40 under the control of processor 44. Thestimulation energy generated by therapy module 42 may be delivered fromtherapy module 42 to selected electrodes 40 via a switching module andconductors carried by lead 16, as controlled by processor 44.

Processor 44 may include any one or more of a microprocessor, acontroller, a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a field programmable gate array (FPGA),discrete logic circuitry, or the like, and the functions attributed toprocessor 44 may be embodied as software, firmware, hardware or anycombination thereof. Processor 44 controls therapy delivery module 42 todeliver PNFS according to a selected one or more of therapy programs 52stored in memory 46. In the example shown in FIG. 2A, processor 44controls therapy module 42 to deliver electrical pulses with theamplitudes, pulse widths, frequency, or electrode polarities specifiedby the selected one or more therapy programs 52, which may, in someexamples, be arranged into program groups. In one example, processor 44controls therapy module 42 to deliver stimulation therapy according toone therapy program or program group at a time. In another example,therapy programs are stored within at least one of clinician programmer22 or patient programmer 28, which transmits the therapy programs to IMD14 via telemetry module 50. Telemetry module 50 allows processor 44 tocommunicate with clinician programmer 22, patient programmer 28 oranother computing device.

During a trial session, which may occur after implantation of IMD 14 orprior to implantation of IMD 14, a clinician may determine the therapyparameter values that provide efficacious therapy to patient 12.Processor 44 may control therapy module 42 based on information providedby clinician programmer 22, patient programmer 28 or another computingdevice. For example, the clinician may interact with clinicianprogrammer 22 to select a particular therapy program and clinicianprogrammer 22 may transmit a control signal to IMD 14, which is receivedby telemetry module 50 of IMD 14. The control signal may cause processor44 to control therapy module 42 to deliver therapy based on theparameter values specific by the clinician-selected therapy program. Asanother example, clinician programmer 22, patient programmer 28 oranother computing device may utilize a search algorithm thatautomatically selects therapy programs for trialing. The searchalgorithm that automatically elects therapy programs for trialing mayutilize one or more physiological parameters of patient sensed bysensing module 20 (FIG. 1) to select one or more stimulation parametervalues for therapy delivery to patient 12.

Memory 46 may include any volatile, non-volatile, magnetic, optical, orelectrical media, such as a random access memory (RAM), read-only memory(ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM(EEPROM), flash memory, and the like. Memory 46 may store programinstructions that, when executed by processor 44, cause IMD 14 toperform the functions ascribed to IMD 14 herein. In addition to storingprograms 52, memory 46 may also store control information 54, which mayinclude information associating a characteristic of a physiologicalsignal with a control action, such as activating or deactivatingdelivery of PNFS by therapy module 42 or initiating the modification ofa therapy program that defines the stimulation parameter values.

The physiological signal characteristic may include, for example, anamplitude of the physiological signal waveform, a trend in thephysiological signal waveform, a power level of the physiological signalmeasured in a particular frequency band of the physiological signalwaveform, or a ratio of power levels between different frequency bands.In some examples, the physiological signal received from sensing device20 may be compared against a threshold value in order to determinewhether the physiological signal characteristic is present. Thethreshold comparison may, for example, be used to determine a change inthe physiological signal compared to a baseline of that signal, whichmay be previously determined or may be a reference or control signalfrom a second sensor (e.g., as shown and described with respect to FIGS.16 and 17). In other examples, the physiological signal may be comparedto a template in order to determine whether the physiological signalcharacteristic is present in the signal from sensing module 20.

As described with respect to FIG. 6, processor 44 may use controlinformation 54 to control therapy module 42. In some examples, memory 46may also store patient physiological data (such as sensed physiologicalsignals) obtained by IMD 14 or sensing module 20. Memory 46 may have anysuitable architecture. For example, memory 46 may be partitioned tostore therapy programs 52 and control information 54. Alternatively,therapy programs 52 and control information 54 may each be stored inseparate memories that are linked to processor 44.

Power source 48 may take the form of a small, rechargeable ornon-rechargeable battery, or an inductive power interface thattranscutaneously receives inductively coupled energy. In the case of arechargeable battery, power source 48 similarly may include an inductivepower interface for transcutaneous transfer of recharge power.

FIG. 2B is a functional block diagram of another example IMD 56, whichis substantially similar to IMD 14, but includes a sensing module. Aspreviously described, in some examples, sensing module 20 (FIG. 1) maybe incorporated within a common outer housing with a therapy module ofIMD 14, as shown in FIG. 2B. IMD 56 may include a therapy module and asensing module 58 that senses a patient parameter via at least some ofthe electrodes 40. For example, some of electrodes 40 (or a separate setof sensing electrodes) may be used to generate an EMG signal thatindicates muscle activity within region 18 of patient 12. The sensedparameter signals generated by therapy and sensing module 58 may bestored within memory 46.

In other examples, one or more additional sensors may be incorporatedwith IMD 56, e.g., on a housing of IMD 56 that encloses therapy andsensing module 58, processor 44, memory 46, power source 48, andtelemetry module 50. In addition, in some examples, IMD 56 maycommunicate with an external sensing module 20 that senses the same or adifferent patient parameter than therapy and sensing module 58. WhileIMD 14 and sensing module 20 of FIG. 1 are primarily referred tothroughout the description, in other examples, the disclosure is alsoapplicable to systems including IMD 56 with therapy and sensing module58.

FIG. 3 is a functional block diagram illustrating components of anexample clinician programmer 22, which includes processor 60, memory 62,user interface 64, telemetry module 66, and power source 68. Processor60 controls user interface 64 and telemetry module 66, and stores andretrieves information and instructions to and from memory 62. Clinicianprogrammer 22 may be a dedicated hardware device with dedicated softwarefor programming of IMD 14. Alternatively, clinician programmer 22 may bean off-the-shelf computing device running an application that enablesprogrammer 22 to program IMD 14.

A clinician may use clinician programmer 22 to select therapy programs(e.g., sets of stimulation parameters), generate new therapy programs,modify therapy programs through individual or global adjustments ortransmit the new programs to a medical device, such as IMD 14 (FIG. 1).The clinician may interact with programmer 22 via user interface 64,which includes display 24 and keypad 26. Keypad 26 may include anysuitable mechanism for receiving input from the clinician or anotheruser. In one example, keypad 26 includes an alphanumeric keypad. Inanother example, keypad 26 includes a limited set of buttons that arenot necessarily associated with alphanumeric indicators. For example,the limited set of buttons may include directional buttons that permitthe clinician to scroll up, down, or sideways through a displaypresented on display 24, select items shown on display 24, as well asenter information. The limited set of buttons may also include“increment/decrement” buttons in order to increase or decrease astimulation frequency or amplitude of stimulation delivered by IMD 14.

Keypad 26 may include, and/or respond to, any one or more of pushbuttons, soft-keys that change in function depending upon the section ofthe user interface currently viewed by the user, voice activatedcommands, physical interactions, magnetically triggered functions,password authentication push buttons, contacts defined by a touchscreen, or any other suitable user interface. In some examples, buttonsof keypad 26 may be reprogrammable. That is, during the course of use ofclinician programmer 22, the buttons of keypad 26 may be reprogrammed toprovide different programming functionalities as the needs of theclinician or if the type of IMD 14 implanted within patient 12 changes.Clinician programmer 22 or another computing device may includefunctions for reprogramming keypad 26.

As previously discussed, display 24 may include a color or monochromedisplay screen, such as a LCD or LED display. Clinician programmer 22may present information related to stimulation therapy provided by IMD14, as well as other information, such as historical data regarding thepatient's condition and past event information. Processor 60 monitorsactivity from keypad 26, and controls display 24 and/or IMD 14 functionaccordingly. In some examples, display 24 may be a touch screen thatenables the user to select options directly from the display. In suchcases, keypad 26 may be eliminated, although clinician programmer 22 mayinclude both a touch screen and keypad 26. In some examples, userinterface 64 may also include audio circuitry for providing audibleinstructions or sounds to a user and/or receiving voice commands fromthe user.

Processor 60 may comprise any combination of one or more processorsincluding one or more microprocessors, DSPs, ASICs, FPGAs, or otherequivalent integrated or discrete logic circuitry. Accordingly,processor 60 may include any suitable structure, whether in hardware,software, firmware, or any combination thereof, to perform the functionsascribed herein to processor 60. Memory 62 may include any volatile ornonvolatile memory, such as RAM, ROM, EEPROM or flash memory. Memory 62may also include a removable memory portion that may be used to providememory updates or increases in memory capacities. A removable memory mayalso allow patient data to be easily transferred to patient programmer28, or to be removed before clinician programmer 22 is used to programPNFS therapy for a different patient.

Memory 62 stores, among other things, control information 70, therapyprograms 72, and operating software 74. Memory 62 may have any suitablearchitecture. For example, memory 62 may be partitioned to store controlinformation 70, therapy programs 72, and operating software 74.Alternatively, control information 70, therapy programs 72, andoperating software 74 may each be stored within separate memories thatare linked to processor 60. Control information 70 may be similar to thecontrol information 54 stored in memory 46 of IMD 14 (FIG. 2A).

Therapy programs portion 72 of memory 62 stores data relating to thetherapy programs implemented by IMD 14. In some examples, the actualsettings for the therapy programs, e.g., the stimulation amplitude,pulse rate, pulse frequency and pulse width data, are stored withintherapy programs 72. In other examples, an indication of each therapyprogram or group of therapy programs, e.g., a single value associatedwith each therapy program or group, may be stored within therapyprograms 72, and the actual parameters may be stored within memory 46 ofIMD 14. The “indication” for each therapy program or group may include,for example, alphanumeric indications (e.g., Therapy Program Group A,Therapy Program Group B, and so forth), or symbolic indications.

In general, during a programming session, a clinician may select valuesfor a number of programmable therapy parameters with the aid ofclinician programmer 22 in order to define the electrical stimulationtherapy to be delivered by IMD 14 to patient 12. For example, theclinician may select a combination of electrodes carried by one or moreimplantable leads, and assigns polarities to the selected electrodes orset partial activation of electrodes in examples in which electrodes 40of lead 16 (FIG. 2A) may be partially activated. In addition, theclinician may select an amplitude, which may be a current or voltageamplitude, a pulse width, and a pulse rate, in the case of an IMD 14that delivers stimulation pulses to patient 12. A group of parametervalues, including electrode configuration (electrode combination andelectrode polarity), amplitude, pulse width and pulse rate, may bereferred to as a therapy program in the sense that they drive theneurostimulation therapy to be delivered to the patient.

In some examples, the clinician may also provide information such asparameters for the IMD 14 control algorithm, such as stimulationparameter value thresholds of stimulation for patient 12 that indicate atolerable range of PNFS, thresholds for the physiological signalcharacteristics that are used to control IMD 14 based on signals fromsensing module 20 (or another sensing module that may be incorporatedwithin a common housing as IMD 14), time delays or loop updatefrequencies for therapy delivery, or preferences for patient control(e.g., enabling or disabling a patient override of the control of system10 based on physiological signals that may indicate a physiologicaleffect of the PNFS).

Programs selected during a programming session using clinicianprogrammer 22 may be transmitted to and stored within one or both ofpatient programmer 28 and IMD 14. Where the programs are stored inpatient programmer 28, patient programmer 28 may transmit the programsselected by patient 12 to IMD 14 for delivery of PNFS therapy to patient12 according to the selected program. Where the programs are stored inIMD 14, patient programmer 28 may receive a list of programs from IMD 14to display to patient 12, and transmit an indication of the selectedprogram to IMD 14 for delivery of PNFS therapy to patient 12 accordingto the selected program.

During a programming session, which may also be referred to as a therapyprogram trial session, the clinician may specify a program usingclinician programmer 22 by selecting values for various therapyparameters. When a program is specified, the clinician may test theprogram by directing clinician programmer 22 to control IMD 14 todeliver therapy according to the program to patient 12. The clinician orpatient may enter rating information into the programming device foreach tested program. The rating information for a tested program mayinclude information relating to effectiveness of delivery of stimulationtherapy according to the program in treating symptoms of the patient,side effects experienced by the patient due to the delivery ofneurostimulation therapy according to the program, or both. In the caseof stimulation therapy to manage pain, efficacy information may includean indication of the patient's activity level or a subjective rating ofpain relief. If therapy system 10 provides PNFS to manage pain, controlinformation 70 stored in memory 62 of clinician programmer 22 mayinclude physiological parameter values that are associated with aparticular patient pain state.

During the programming session, multiple therapy programs may be tested.That is, during a programming session, IMD 14 may deliver therapy topatient 12 according to a first therapy program, followed by a secondtherapy program, and so forth, in order to assess the efficacy of eachtherapy program. Clinician programmer 22 may maintain a session log thatincludes a listing of programs tested on patient 12, rating informationprovided by the clinician or patient 12 for programs of the list, andcontrol information, such as information that associates a particularpatient parameter value with a positive patient response to therapy(e.g., an improvement from the patient's baseline state). The listing oftrialed therapy programs may be ordered according to the ratinginformation in order to facilitate the selection of programs from thelist by the clinician.

Operating software 74 may include instructions executable by processor60 for operating user interface 64, telemetry module 66, and managingpower source 68. Memory 62 may also store any therapy data retrievedfrom IMD 14 during the course of therapy and store any data receivedfrom patient programmer 28. The clinician may use this therapy data todetermine the progression of the patient's disease in order to predictor plan a future treatment.

Clinician programmer 22 may communicate via wireless telemetry with IMD14, such as using RF communication or proximal inductive interaction.This wireless communication is possible through the use of telemetrymodule 66. Accordingly, telemetry module 66 may be similar to telemetrymodule 50 of IMD 14. Telemetry module 66 may also be configured tocommunicate with patient programmer 28 or another computing device viawireless communication techniques, or direct communication through awired connection. Examples of local wireless communication techniquesthat may be employed to facilitate communication between clinicianprogrammer 22 and another computing device include RF communicationaccording to the 802.11 or Bluetooth specification sets, infraredcommunication, e.g., according to the IrDA standard, or other standardor proprietary telemetry protocols. In this manner, other externaldevices may be capable of communicating with clinician programmer 22without needing to establish a secure wireless connection.

Power source 68 delivers operating power to the components of clinicianprogrammer 22. Power source 68 may include a battery and a powergeneration circuit to produce the operating power. In some examples, thebattery may be rechargeable to allow extended operation. Recharging maybe accomplished by electrically coupling power source 68 to a cradle orplug that is connected to an alternating current (AC) outlet. Inaddition, recharging may be accomplished through proximal inductiveinteraction between an external charger and an inductive charging coilwithin clinician programmer 22. In other examples, traditional batteries(e.g., nickel cadmium or lithium ion batteries) may be used. Inaddition, clinician programmer 22 may be directly coupled to analternating current outlet to recharge power source 68, or to powerclinician programmer 22. Power source 68 may include circuitry tomonitor power remaining within a battery. In this manner, user interface64 may provide a current battery level indicator or low battery levelindicator when the battery needs to be replaced or recharged. In somecases, power source 68 may be capable of estimating the remaining timeof operation using the current battery.

FIG. 4 is a functional block diagram illustrating components of patientprogrammer 28, which may be similar to clinician programmer 22. Patientprogrammer 28 may include a processor 80, memory 82, user interface 84,which includes display 30 and keypad 32, telemetry module 86, and powersource 88. Memory 82 stores therapy programs 90, control information 92,and operating software 94. Memory 82 may have any suitable architecture.For example, memory 82 may be partitioned to store control therapyprograms 90, control information 92, and operating software 94.Alternatively, therapy programs 90, control information 92, andoperating software 94 may each be stored within separate memories thatare linked to processor 80. Control information 92 may be similar to thecontrol information 54 stored in memory 46 of IMD 14 (FIG. 2A).

The functions performed by each component of patient programmer 28 shownin FIG. 4 may be similar to the functions described above with referenceto the similar components of clinician programmer 22. However, clinicianprogrammer 22 may include more features than patient programmer 28. Forexample, clinician programmer 22 may be configured for more advancedprogramming features than patient programmer 28. This may allow a userto modify more therapy parameters with clinician programmer 22 than withpatient programmer 28. Patient programmer 28 may have a relativelylimited ability to modify therapy parameters of IMD 14 in order tominimize the possibility of patient 12 selecting therapy parameters thatmay be harmful to patient 12. Similarly, clinician programmer 22 mayconduct more advanced diagnostics of IMD 14 than patient programmer 28.

Patient 12 may interact with patient programmer 28 via user interface84, which includes display 30 and keypad 32. Patient 12 may inputinformation via user interface 84 relating to the therapeutic efficacyof a therapy program or a patient state during therapy delivery by IMD14 according to a particular therapy program. In some cases, patientprogrammer 28 provides patient 12 with an option of enabling ordisabling automatic control of IMD 14, or override it with otherpreferences, e.g., depending on the patient's pain state. Theinformation relating to the patient state may be used to control therapydelivery by IMD 14. As described in further detail below, patient 12 mayinput information indicating a patient pain state via user interface 84.The patient pain state information may then be used to control therapydelivery by IMD 14.

It is believed that delivery of PNFS by IMD 14 generates a detectablechange in a physiological parameter of patient 12 that indicates thephysiological effect of the PNFS on patient 12. In order to maintainefficacious PNFS therapy, it may be desirable for IMD 14 to deliver PNFSto patient 12 to maintain the physiological effect, or, in some cases,avoid the physiological effect if the physiological effect is anundesirable side effect. In some examples, the physiological effect ismaintained by controlling the PNFS such that an amplitude or energylevel in one or more frequency bands of a physiological signal remainsat a certain level, within a range of values, below a certain level orabove a certain level, depending on the physiological parameter. Thedesired level of the physiological signal characteristic may bedetermined based on information received during a programming session inwhich patient input regarding therapeutic efficacy (e.g., balance ofbeneficial results and side effects) is received in response to therapydelivery and associated with a physiological signal characteristic. Inother examples, desired level of the physiological signal characteristicmay be determined based on a control signal from a second sensing module(shown in FIG. 16), which indicates a desirable value for thephysiological signal characteristic.

As another example, the physiological effect may be maintained bycontrolling PNFS such that a physiological signal waveform maintainssome trend (e.g., a particular slope), which may depend upon the type ofphysiological effect. Accordingly, processor 44 of IMD 14 may controltherapy module 42 based on a physiological signal generated by sensingmodule 20.

While processor 44 of IMD 14 is primarily referred to in the descriptionof FIGS. 5-9, in other examples, processor 60 of clinician programmer22, processor 80 of patient programmer, or a processor of another devicemay control therapy module 42 based on a physiological signal generatedby sensing module 20. Furthermore, while the reminder of the descriptionprimarily refers to IMD 14 and a separate sensing module 20, in otherexamples, therapy system 10 may be controlled based on a physiologicalsignal that is sensed by an IMD (e.g., IMD 56 in FIG. 2B) in addition toor instead of the signal generated by sensing module 20.

FIG. 5 is a flow diagram illustrating an example technique forcontrolling therapy system 10 based on a sensed physiological parameterof patient 12 that indicates the physiological effects (e.g., anefferent response) of the PNFS on patient 12. Processor 44 controlstherapy module 42 to deliver PNFS to region 18 (FIG. 1) of patient 12according to a therapy program (96). For example, processor 44 mayselect a therapy program from memory 46 of IMD 14 and control therapymodule 42 to generate and deliver according to the selected therapyprogram. As another example, processor 44 may control therapy module 42to deliver PNFS according to a clinician-selected therapy program. Inone example, the clinician may select the therapy program from a list oftherapy programs stored in clinician programmer 22 (FIG. 3) byinteracting with user interface 64. Processor 60 of clinician programmer22 may then transmit a control signal to processor 44 of IMD 14 by thetelemetry module 66 of clinician programmer 22. The control signal mayset forth the parameter values of the therapy program or may merely bean identifier associated with the therapy program, and the actualparameter values may be stored within memory 46 of IMD 14 and associatedwith the identifier in memory 46.

In another example, processor 44 controls therapy module 42 to deliverPNFS according to a patient-selected therapy program. For example,patient 12 may select the therapy program from a list of therapyprograms stored in memory 82 of patient programmer 28 (FIG. 4) byinteracting with user interface 84. Processor 80 of patient programmer28 may then transmit a control signal to processor 44 of IMD 14 via therespective telemetry modules 86 (FIG. 4), 50 (FIG. 2A). Again, thecontrol signal may define the therapy parameter values or may merely bean identifier associated with a therapy program that is stored in IMD14.

Processor 44 monitors a physiological parameter of patient 12, such asby receiving a physiological signal from sensing module 20 (FIG. 1)(98). As previously indicated, the physiological signal may indicate anefferent response of the patient to the PNFS. Processor 44 controlstherapy module 42 based on the monitored physiological parameter ofpatient 12 (100). In some examples, processor 44 activates or deactivatetherapy delivery or modifies the therapy program, e.g., if processor 44determines that the physiological signal indicates the therapy programis not efficacious or does not meet a certain level of efficacy.

In this way, the patient's efferent response to PNFS, detected bymonitoring a physiological parameter of patient 12, may be used in aclosed-loop therapy system in order to control the therapy delivery. Thedetected efferent response may be incidental to the PNFS because IMD 14may deliver PNFS to patient 12 to generate an afferent response, and mayincidentally activate efferent nerves, thereby resulting in an efferentresponse from the patient. Examples of efferent responses include musclecontractions, a change in blood flow, activation of the sweat glands ora pilomotor reflex response (e.g., goose bumps).

In some examples, processor 44 monitors more than one physiologicalparameter of patient 12 at a time (98) and control therapy delivery bytherapy module 42 (FIG. 2) based on the plurality of monitoredphysiological parameters. For example, processor 44 may receive morethan one physiological signal from sensing module 20, whereby thedifferent signals indicate the activity of respective physiologicalparameters. Processor 44 may control the delivery of therapy to patient12 to maintain a physiological effect that is based on the plurality ofmonitored physiological parameters. For example, processor 44 maycontrol the delivery of PNFS such that respective signal characteristicsof the one or more physiological parameters remain within respectiveranges, at respective levels, above or below respective levels(depending upon the type of physiological parameter), at some levelrelative to respective control signals, exhibit respective predeterminedtrends, and the like. For example, processor 44 may control therapymodule 42 to deliver PNFS to region 18 such that a physiological signalindicative of the blood flow rate through region 18 is increased, but isnot increased so high that an amplitude of another physiological signalindicative of a pilomotor response is greater than or equal to athreshold value.

In some examples, the plurality of monitored physiological parametersmay be weighted, such that processor 44 may assign a higher priority tocontrolling PNFS therapy to control a particular physiological parameterof the plurality of monitored physiological parameters.

In various examples, processor 44 may perform template matching, peakdetection, or threshold amplitude or energy level value comparisons inorder to determine the patient's physiological response to the PNFS andcontrol therapy. Example techniques processor 44 may employ to determinethe patient's response to PNFS are described with reference to FIGS.6-9.

FIG. 6 is a flow diagram illustrating an example technique forcontrolling therapy system 10 based on an amplitude of a physiologicalsignal. Just as in the technique shown in FIG. 5, processor 44 of IMD 14controls the delivery of PNFS therapy to patient 12 according to atherapy program (96). Processor 44 receives a physiological signal fromsensing module 20 (102). As therapy is delivered to patient 12,processor 44 determines a physiological effect on patient 12 bycomparing an amplitude of the received physiological signal to athreshold value (104). The threshold value may be stored within controlinformation portion 54 of memory 46 or may be determined based on acontrol physiological signal that indicates the activity of thephysiological parameter in another region of the patient's body that isoutside of region 18 (FIG. 1) to which PNFS is delivered. The lattertechnique for determining a threshold value based on a controlphysiological signal is described below with reference to FIGS. 16 and17. The control physiological signal may be generated by a controlsensing module that is separate from sensing module 20 or may begenerated by sensing module 20 or IMD 14.

In one example, processor 44 samples the physiological signal, e.g.,using a 5 ms to a 10 second time window, and compares a peak, average ormedian amplitude during the sample time window to the threshold window(104). The time window may be selected based on the cycle of theselected physiological parameter. For example, when monitoringrespiratory rate, the window may be about 3 seconds to about 10 secondsbecause a respiratory cycle may take about 3 seconds to about 10seconds, although other cycles are contemplated. As another example,when monitoring muscle activity via EMG signals, the EMG signals maychange relatively fast (e.g., within about 5 ms to about 10 ms ofproviding PNFS). Processor 44 may perform the amplitude-thresholdcomparison at any suitable frequency, such as about 0.1 Hertz (Hz) toabout 15 Hz or greater. For example, some examples of processor 44 mayperform the amplitude-threshold comparison at a frequency of up to 500Hz.

In one example, a desired therapeutic effect may be associated with aparticular characteristic of a physiological parameter of the patient,and therapy may be delivered to the patient until the physiologicalparameter characteristic is detected. If processor 44 determines thatthe amplitude of the physiological signal is greater than or equal tothe threshold value (106), processor 44 may determine that the patient'sresponse to the delivery of PNFS was positive, e.g., IMD 14 providedefficacious therapy. Accordingly, processor 44 deactivates the deliveryof PNFS if the amplitude of the physiological signal is greater than orequal to the threshold value (108). Processor 44 may then continuemonitoring the physiological signal (102) and comparing the signalamplitude to the threshold value in order to determine when the positivephysiological effects of the PNFS have substantially dissipated, asindicated by a signal amplitude value that is not greater than or equalto a threshold value. At that time, processor 44 initiates the deliveryof PNFS therapy according to the therapy program (110). In otherexamples, rather than deactivating the delivery of PNFS (108), processor44 decreases the intensity of stimulation, such as by decreasing anamplitude of the electrical stimulation signal defined by the therapyprogram or the duration of the signal, or modifying the frequency, dutycycle or pulse width of the stimulation signal.

Rather than delivering continuous PNFS to patient 12, processor 44controls therapy module 42 to provide therapy to patient as needed,i.e., on-demand, based on the physiological signal indicative of theeffects of the PNFS. The on-demand therapy may be a more efficient useof power source 48 (FIG. 2A) of IMD 14 compared to continuous deliveryof PNFS. In addition, the therapy delivery technique described withrespect to FIGS. 5 and 6, as well as the techniques described withrespect to FIGS. 7-9, may help reduce the possibility or speed at whichpatient 12 adapts to the PNFS therapy. It has also been found thatpatient 12 may adapt to PNFS provided by IMD 14 over time. That is, acertain level of electrical stimulation provided to region may be lesseffective over time. This phenomenon may be referred to as “adaptation”or “accommodation.” As a result, any beneficial effects to patient 12from the PNFS may decrease over time. While the electrical stimulationlevels (e.g., amplitude of the electrical stimulation signal) may beincreased to overcome such adaptation, the increase in stimulationlevels may consume more power, and may eventually reach undesirable orharmful levels of stimulation.

If processor 44 determines that the amplitude of the physiologicalsignal is not greater than or equal to the threshold value (106),processor 44 may determine that the therapeutic effects of the PNFS havenot been achieved yet. Accordingly, processor 44 controls therapy module42 to continue delivering PNFS according to the therapy program (110).Processor 44 may continue monitoring the physiological signal andcomparing the signal to the threshold value to determine when todeactivate the PNFS (108).

In other examples, rather than determining a physiological effect of thePNFS therapy on patient 12 as the PNFS is delivered to patient 12,processor 44 may control the delivery of therapy to patient 12 for aparticular time period, such as 30 seconds to an hour or more, anddetermine the physiological effect after the PNFS delivery time period(i.e., the “stimulation period”) and while the delivery of PNFS topatient 12 is suspended. If, after the stimulation period, the amplitudeof the physiological signal is less than the threshold value, processor44 may control therapy module 42 to deliver therapy to patient 12 for asubsequent stimulation period. After the subsequent stimulation period,processor 44 may compare the amplitude of a received physiologicalsignal to the threshold value. In this way, processor 44 may controltherapy delivery based on a cycle including a stimulation periodfollowed by an analysis time period during which PNFS is not deliveredor has a reduced intensity to assess the patient's physiologicalresponse to the therapy.

In another example of FIG. 6, rather than deactivating therapy if theamplitude of the physiological signal is greater than or equal to thethreshold value, processor 44 may deactivate therapy if the amplitude ofthe physiological signal is within an acceptable range of values, whichmay also be stored within control information 54 portion of memory 46.

Furthermore, although in FIG. 6, processor 44 determines thattherapeutic effects of the PNFS are present when the amplitude of thephysiological signal is greater than or equal to a threshold value, inother examples, depending on the type of physiological signal, processor44 may determine that therapeutic effects of the PNFS are present whenthe amplitude is greater than the threshold value, or less than thethreshold value or less than or equal to the threshold value. Forexample, if therapy system 10 is implemented to mitigate pain due toback spasms, the physiological signal may indicate EMG activity ofregion 18 (FIG. 1). Processor 44 may determine that positivephysiological effects of the PNFS are observed when the back spasms havesubsided, which may be associated with a physiological signal amplitudeless than or equal to the threshold value.

In some cases, a selected therapy program may be ineffective. Forexample, as discussed above, in some cases, patient 12 may adapt to PNFSand the intensity of stimulation (e.g., the amplitude or anotherstimulation parameter) may be increased in order to maintain therapeuticeffects. FIG. 7 is a flow diagram of an example technique for modifyinga therapy program based on detected physiological effects of PNFS. Thetechnique shown in FIG. 7 is similar to the technique shown in FIG. 6.However, after determining that the amplitude of the physiologicalsignal is not greater than or equal to the threshold amplitude value(106), processor 44 generates and stores an efficacy indication, whichmay be a value, flag, or signal that is stored or transmitted toindicate the therapy program was not effective (112).

Different patients may respond differently to PNFS. For some patients,therapeutic effects of the therapy delivery may not be immediate, andmay be observed after PNFS is delivered for a particular time period,such as a few minutes, a few hours or even a day or more. Accordingly,processor 44 may not immediately modify a therapy program if therapeuticeffects are not observed. Instead, processor 44 may compare a totalefficacy indication count, which may be stored in memory 46 of IMD 14 ora memory of another device, to a count threshold value, which may alsobe stored in memory 46 or another device. In some examples, thethreshold efficacy count for triggering the modification to the therapyprogram may be selected by the clinician.

If the efficacy indication count does not exceed the count threshold(114), processor 44 may continue delivering PNFS therapy according tothe selected therapy program (110) and monitoring the physiologicalsignal (102) to determine if a physiological response of patient 12indicates the PNFS was efficacious. The efficacy count may reflect thetotal number of efficacy indications within a particular time period,such as the entire duration the therapy was delivered according to thetherapy program or a more limited time period, such as a day or more.

On the other hand, if the efficacy indication count is greater than orequal to the count threshold (114), processor 44 determines that theselected therapy program is not efficacious. Accordingly, processor 44modifies the therapy program (116) if the efficacy count exceeds (or isgreater than or equal to) the threshold. Processor 44 may modify thetherapy program using any suitable technique. In one example, processor44 selects another therapy program from memory 46. For example, thetherapy programs 52 stored in memory 446 may be ordered according totheir relative efficacy. Processor 44 may select the next-best therapyprogram from the stored therapy programs 52 upon determining that thecurrent therapy program is ineffective.

In another example, processor 44 may notify processor 60 of clinicianprogrammer 22 (FIG. 3) that a modification to the therapy program isdesirable, and processor 60 of programmer 22 may implement a methodicalsystem to identify another set of potentially beneficial therapyparameter values for patient 12. In one example, processor 60 mayimplement a tree-based technique for selecting the therapy program. Aprogramming tree structure may include a plurality of levels that areassociated with a different therapy parameter. The tree may includenodes that are connected to nodes of adjacent levels. A clinician orpatient 12 may interact with processor 60 via user interface 64 (FIG. 3)in order to create a program path by moving through one node at eachlevel of the tree according to efficacy feedback from patient 12 and/orone or more sensors that detect physiological parameters of patient 12,such as sensing module 20.

Examples of tree-based techniques for modifying a therapy program orgenerating a new therapy program are described in commonly-assigned U.S.patent application Ser. No. 11/799,114 to Gerber et al., entitled,“TREE-BASED ELECTRICAL STIMULATION PROGRAMMING FOR PAIN THERAPY,” andfiled on Apr. 30, 2007; commonly-assigned U.S. patent application Ser.No. 11/799,113 to Gerber et al., entitled, “TREE-BASED ELECTRICALSTIMULATOR PROGRAMMING,” and filed on Apr. 30, 2007; andcommonly-assigned U.S. patent application Ser. No. 11/414,527 to Gerberet al., entitled, “TREE-BASED ELECTRICAL STIMULATOR PROGRAMMING,” andfiled on Apr. 28, 2006, which are each incorporated herein by referencein their entireties.

In another example, processor 60 of clinician programmer 22 mayimplement a genetic algorithm-based technique for modifying the therapyprogram, such as the one described in commonly-assigned U.S. Pat. No.7,239,926 to Goetz et al., entitled, “SELECTION OF NEUROSTIMULATIONPARAMETER CONFIGURATIONS USING GENETIC ALGORITHMS,” which issued on Jul.3, 2007 and is incorporated herein by reference in its entirety. In oneexample described in U.S. Pat. No. 7,239,926 to Goetz et al., geneticalgorithms guide the selection of stimulation parameter values bysuggesting the parameter values that are most likely to be efficaciousgiven the results of tests already performed during an evaluation (orprogramming) session. Genetic algorithms encode potential solutions to aproblem as members of a population of solutions. This population is thenjudged based on a fitness function. The best performers, i.e., the bestfit solutions, are then retained and a new generation is created basedupon their characteristics. The new generation is composed of solutionssimilar in nature to the best performers of the previous generation.

Other suitable techniques for selecting a therapy program include thosedescribed in U.S. Pat. No. 7,184,837 to Goetz, entitled, “SELECTION OFNEUROSTIMULATOR PARAMETER CONFIGURATIONS USING BAYESIAN NETWORKS,” whichwas filed on Jan. 29, 2004 and is incorporated herein by reference inits entirety. As described in U.S. Pat. No. 7,184,837 to Goetz,processor 60 of clinician programmer 22 or another device, or aclinician may execute a parameter configuration search algorithm thatrelies on a Bayesian network structure that encodes conditionalprobabilities describing different states of the parameterconfiguration. The Bayesian network structure may provide a conditionalprobability table that represents causal relationships between differentparameter configurations and clinical outcomes. The search algorithmuses the Bayesian network structure to infer likely efficacies ofpossible parameter configurations based on the efficacies of parameterconfigurations already observed.

Processor 60 of clinician programmer 22 may transmit the modifiedtherapy program to IMD 14, and processor 44 of IMD 14 may controltherapy module 42 to deliver PNFS therapy to patient 12 according to themodified therapy program (116). Processor 44 may then monitor thephysiological effects of the PNFS according to the modified program bymonitoring the physiological signal (102) and comparing the signal to athreshold (106). The technique shown in FIG. 7 may then be implementedfor the modified therapy program.

In some examples, processor 44 generates a notification to alert patient12 that the therapy program was modified. For example, processor 44 maytransmit an alert to patient programmer 28 via telemetry module 50 thatis provided to patient 12 via user interface 84 of patient programmer 28(FIG. 4). The alert may be a visual, auditory or somatosensory (e.g.,vibration) alert. In addition, processor 44 may record the therapymodification in memory 46 or in memory 82 of patient programmer 28 oranother device for later analysis by the clinician.

FIG. 8 is a flow diagram of an example technique for controlling therapysystem 10 based on a pattern in a physiological signal waveform, wherethe pattern is indicative of the therapeutic efficacy of the PNFS. Justas with the techniques shown in FIGS. 6 and 7, processor 44 of IMD 14controls therapy module 42 to deliver PNFS therapy according to atherapy program (96) and receives a physiological signal from sensingmodule 20 (102).

As previously indicated, processor 44 may control therapy module 42 todeliver PNFS in order to maintain a particular a physiological effect ofthe PNFS. In the example technique shown in FIG. 8, the physiologicaleffect is characterized by one or more characteristics (e.g., a pattern)of a physiological signal waveform. Accordingly, during or after astimulation period during which therapy module 42 delivers PNFS topatient 12, processor 44 compares a physiological signal waveform to atemplate (118) in order to determine whether to continue delivering PNFSor to deactivate PNFS. The template may be stored in control information54 portion of memory 46 of IMD 14. In some examples, the template isdetermined during a programming session in which a clinician associatesa physiological signal characteristic (e.g., the template) with adesirable physiological response or an undesirable physiologicalresponse. In other examples, the template is determined based on acontrol physiological signal that indicates the activity of thephysiological parameter of the patient in a region outside of the region18 in which patient 12 feels pain.

In one example, processor 44 implements a temporal correlationtechnique, during which processor 44 samples the physiological signalwaveform with a sliding window and compares the sample to a template todetermine whether the sampled signal correlates well with the template.For example, processor 44 may perform a correlation analysis by moving awindow along a digitized plot of the amplitude of the measuredphysiological signals at regular intervals, such as between about 1 msto about 1 second intervals, to define a sample of the physiologicalsignal. The sample window may be slid along the plot of thephysiological signal waveform until a correlation is detected betweenthe waveform of the baseline template and the waveform of the sample ofthe physiological signal defined by the window.

By moving the window at regular time intervals, multiple sample periodsare defined. The correlation may be detected by, for example, matchingmultiple points between the template waveform and the waveform of theplot of the physiological signal over time, or by applying any suitablemathematical correlation algorithm between the sample in the samplingwindow and a corresponding set of samples stored in the templatewaveform. As examples, if rate of change (i.e., the slope) of themonitored physiological signal correlates to the slope of a trendtemplate, the physiological signal may indicate the presence of positivetherapeutic effects of the PNFS therapy. As another example, ifinflection points in the physiological signal waveform substantiallycorrelate to a template, the physiological signal may indicate thepresence of positive therapeutic effects of the PNFS therapy.

If the pattern in the physiological signal waveform substantiallymatches the template (120), processor 44 deactivates the delivery ofPNFS (108) until the physiological signal indicates therapy delivery isdesirable, e.g., a pattern of the physiological signal waveform nolonger matches the template. In some examples, the template matchingalgorithm that processor 44 employs to determine whether the pattern inthe physiological signal substantially matches the template may notrequire a one hundred percent (100%) correlation match, but rather mayonly match some percentage of the pattern. For example, if the monitoredphysiological signal exhibits a pattern that matches about 75% or moreof the template, processor 44 may determine that there is a substantialmatch between the pattern and the template.

On the other hand, if the pattern in the physiological signal waveformdoes not substantially match the template (120), processor 44 continuesdelivering PNFS to patient 12 according to the therapy program. In someexamples, processor 44 may generate an efficacy indication and modifythe therapy program if a total count of the efficacy indications exceedsa threshold value, as discussed with respect to FIG. 7.

In other examples, rather than deactivating the delivery of PNFS (108),processor 44 may decrease the intensity of stimulation, such as bydecreasing an amplitude of the electrical stimulation signal defined bythe therapy program, decreasing the duration of the stimulation signal,decreasing the frequency, or changing the pulse burst pattern. Inaddition, in the technique shown in FIG. 8, processor 44 deactivatestherapy delivery if the physiological signal waveform matches atemplate, while in other examples, processor 44 decreases the intensityof PNFS provided to region 18. In other examples, however, processor 44deactivates therapy delivery if the physiological signal waveform doesnot match a template and continues controlling therapy module 42 todeliver PNFS to region 18 of patient 12 if the waveform matches thetemplate.

FIG. 9 is a flow diagram of an example technique for controlling therapysystem 10 based on a frequency band (or frequency domain) component of aphysiological signal that indicates a patient's physiological responseto the PNFS. Just as with the techniques shown in FIGS. 6-8, processor44 of IMD 14 controls therapy module 42 to deliver PNFS therapyaccording to a therapy program (96) and receives a physiological signalfrom sensing module 20 (102) that changes as a function of a selectedphysiological parameter of patient 12.

Processor 44 analyzes the physiological signal in the frequency domain(122) and compares one or more selected frequency components of thephysiological signal to corresponding frequency components of a templatesignal, which may be stored in memory 46 of IMD 14, a memory of anotherdevice or may be based on a control physiological signal that indicatesthe activity of the selected physiological parameter outside of theregion 18 in which patient 12 feels pain. Either sensing module 20 orprocessor 44 may tune the physiological signal to a particular frequencyband, which may be selected based on the frequency band that is mostrevealing of the physiological effects from PNFS. Processor 44 comparesan energy level within the particular frequency band to a stored valueto determine whether the PNFS resulted in beneficial physiologicaleffects within patient 12 (124). In another example, processor 44compares the ratio of power levels within two or more frequency bands toa stored value. In another example, the correlation of changes of powerbetween frequency bands may be compared to a stored value to determinewhether to deactivate or continue delivery of PNFS.

If the energy level of the physiological signal is greater than or equalto the threshold value (124), processor 44 deactivates the delivery ofPNFS or decreases the intensity of PNFS (108) until the physiologicalsignal indicates therapy delivery is desirable, e.g., the energy levelwithin the selected frequency band is no longer greater than or equal tothe threshold value. On the other hand, if the energy level of thephysiological signal is not greater than or equal to the threshold value(124), processor 44 may continue delivering PNFS to patient 12 accordingto the therapy program (110). In some examples, processor 44 generatesan efficacy indication and modifies the therapy program if a total countof the efficacy indications exceeds a threshold value, as discussed withrespect to FIG. 7.

In the technique shown in FIG. 9, processor 44 may deactivate therapydelivery if the energy level of the physiological signal within one ormore frequency bands is greater than or equal to a threshold value.However, in other examples, processor 44 deactivates therapy delivery ifthe energy level of the physiological signal within one or morefrequency bands is greater than a threshold value, less than thethreshold value, or less than or equal to the threshold value. Ingeneral, in other examples, processor 44 may decrease an intensity ofPNFS delivered to region 18 (FIG. 1), rather than deactivating therapydelivery.

As previously described, in some examples, a characteristic of aphysiological signal may be associated with a physiological effect ofPNFS, which may then be stored as control information to provideclosed-loop control of therapy system 10. The particular physiologicalsignal characteristic (as well as the type of physiological parameter)that indicates a particular physiological effect of the PNFS may bedetermined during a learning stage, such as during a programmingsession. The programming session may utilize an external trialstimulator for delivery of PNFS if the programming session takes placeprior to implantation of IMD 14 within patient 12, or the programmingsession may utilize IMD 14. In other examples, the characteristic of aphysiological signal may be based on a control physiological signal thatchanges as a function of the physiological parameter of the patientoutside of the region 18. Processor 44 may receive the control signalfrom a sensing module that is separate from IMD 14 or may a sensingmodule within the same housing as IMD 14 may generate the controlphysiological signal.

FIG. 10 is a flow diagram illustrating an example technique fordetermining a physiological signal characteristic that indicates apositive patient response to the PNFS. The determined physiologicalsignal characteristic may be stored within memory 46 of IMD 14, memory62 of clinician programmer 22, memory 82 of patient programmer 28 or amemory of another device. While the description of FIG. 10 primarilyrefers to processor 60 of clinician programmer 22 (FIG. 3), in otherexamples, processor 80 of patient programmer 28 (FIG. 4), a processor ofanother device or more than one processor may perform the techniqueshown in FIG. 10. Processor 60 controls the delivery of PNFS therapy topatient 12 according to a therapy program (96). The therapy program mayhave been previously determined to provide efficacious therapy topatient 12. Processor 60 receives a physiological signal (102), e.g.,from sensing module 20 or IMD 14. The physiological signal may change asa function of a physiological parameter that reflects an efferent orautonomic response of patient 12 to the PNFS.

Processor 60 receives input from patient 12 or another user regardingthe efficacy of the PNFS (126). For example, a user may indicate, viauser interface 64 of clinician programmer 22 (FIG. 3) or user interface84 of patient programmer 28 (FIG. 4), when patient 12 feels therapeuticeffects of the PNFS. In response to receiving the input (126), processor60 determines a characteristic of the physiological signal thatcorresponds to the patient input (128). The determined physiologicalsignal characteristic may be used in any technique to control PNFStherapy, such as the techniques described above with respect to FIGS.5-9. In one example, processor 60 determines a peak amplitude, averageamplitude or median amplitude of the physiological signal during a timeperiod that temporally correlates to the patient input, such as within atime range of about one second to about 10 minutes prior to and afterthe patient input was received. However, other time ranges arecontemplated. For example, with some physiological signals, such as arespiratory rate or body temperature, a longer period of time (e.g., onthe order of minutes) may provide results that are more representativeof the patient's current state. The amplitude value may then be storedas the physiological signal characteristic in control information 70portion of memory 62 (FIG. 3) of clinician programmer 22 or a memory ofanother device (130).

In another example, processor 60 determines an acceptable window ofvalues for the physiological signal characteristic by determining thepeak amplitude value and the lowest amplitude value during a time spanof about one second to about 10 minutes prior to and after the patientinput was received. Other time ranges are contemplated. The range ofamplitude values may then be stored as the physiological signalcharacteristic in control information 70 portion of memory 62 ofclinician programmer 22 or a memory of another device (130).

In another example, processor 60 determines a pattern in thephysiological signal waveform that temporally correlates to the patientinput, such as within a time range of about one second to about oneminute prior to and after the patient input was received, although othertime ranges are contemplated. The pattern may then be used as a templatethat is stored as the physiological signal characteristic in controlinformation 70 portion of memory 62 of clinician programmer 22 or amemory of another device (130).

In another example, processor 60 determines an energy level within oneor more frequency bands of the physiological signal waveform thattemporally correlates to the patient input, such as within a time rangeof about one second to about 10 minutes prior to and after the patientinput was received. Again, other time ranges are contemplated. The oneor more energy levels may then be used to define a template that isstored as the physiological signal characteristic in control information70 portion of memory 62 of clinician programmer 22 or a memory ofanother device (130).

In some examples, the patient input may be used during a programmingsession or chronic therapy delivery to determine the physiologicalparameter characteristics that provide control information forcontrolling therapy module 42 of IMD 14 (e.g., to activate or deactivatetherapy, or modify a therapy program). Chronic therapy may refer to theperiod of time during which patient 12 is not in a programming sessionwith the clinician and when IMD 14 is implemented to provide PNFStherapy to patient 12 on a non-temporary basis. Patient 12 may provideinput modifying a therapy program until a physiological effect of thePNFS (e.g., a muscle spasm) reached a tolerable (or, in some cases, anintolerable) level. This input may be used to set the lower or upperthreshold values of the physiological signal characteristic that acts asthe control information in the algorithm that processor 44 of IMD 14 (oranother device) implements in order to control therapy module 42 basedon a monitored physiological parameter of patient 12.

For example, patient 12 may modify one or more therapy parameter valuesof the therapy program until the physiological effect of the PNFSmitigates the patient's pain. A first characteristic of thephysiological signal that is received when patient 12 indicates the PNFSwas effective may be a lower threshold value. Patient 12 may also modifyone or more therapy parameter values of the therapy program until thephysiological effect of the PNFS exceeds a tolerable level, e.g., theside effects of the PNFS begin to outweigh the therapeutic effects. Asecond characteristic of the physiological signal that is received whenpatient 12 indicates the PNFS is no longer tolerable or beneficial maybe an upper threshold value. Processor 44 may then control therapymodule 42 to maintain the physiological signal received from sensingmodule 20 at the determined threshold value, or, in some cases, belowthe threshold value or within the range determined based on the upperand lower threshold values.

As previously described, patient 12 may use patient programmer 28 tomake adjustments to therapy programs, thereby resulting in a modifiedtherapy program. The patient's response to therapy delivery according tothe modified therapy program may be used to determine whether themodified therapy program is suitable for patient 12. For example, thephysiological signal generated by sensing module 20 (FIG. 1) mayindicate that the patient's response to delivery of PNFS according tothe modified therapy program is undesirable. Control information 54stored in IMD 14 (FIG. 2A), control information 70 stored in clinicianprogrammer 22 (FIG. 3) or control information 92 stored in patientprogrammer 28 (FIG. 4) may be used to determine the validity of amodified therapy program.

FIG. 11 is a flow diagram illustrating an example technique fordetermining the usefulness (or validity) of a patient's modification toa therapy program. Processor 44 of IMD 14 controls therapy module 42 todeliver PNFS to patient 12 according to a therapy program (96).Processor 44 receives patient input regarding a modification to atherapy program (132). In some cases, patient 12 may have the perceptionthat the current therapy program is providing ineffective therapy, and,accordingly, patient 12 may modify the current therapy program. Theclinician may program patient programmer 28 to allow patient 12 limitedcontrol over therapy delivery. For example, patient programmer 28 mayonly enable patient 12 to increase or decrease therapy parameter valueswithin a particular range of values that have been determined by theclinician to be beneficial, or at least not harmful, to patient 12. Thepatient's control over the delivery of PNFS may be useful if patient 12engages in different activities that result in different levels of painwithin region 18 (FIG. 1) of the patient's body. If patient 12 providesinput to patient programmer 28 increasing the voltage or currentamplitude value of the current therapy program, patient programmer 28may transmit the patient input to processor 44 of IMD 14 via therespective telemetry modules 86, 50. Patient programmer 28 may, forexample, transmit only the therapy parameter values that were modifiedby patient 12 or programmer 28 may transmit all of the therapy parametervalues for the modified therapy program.

Processor 44 of IMD 14 controls therapy module 42 to deliver PNFS topatient 12 according to the modified therapy program (134). Processor 44may determine the patient's response to the PNFS according to themodified therapy program based on the physiological effects on patient12. In the technique shown in FIG. 11, processor 44 receives aphysiological signal from sensing module 20 (102) and determines whethera characteristic of the physiological signal is within an acceptablerange (136). The acceptable range may indicate a range of values thatreflect an acceptable physiologic response (e.g., a response thatindicates patient 12 is not in pain). In some cases, if thephysiological signal characteristic falls outside of the acceptablerange, the therapy delivery according to the modified therapy programmay be harmful to patient 12. For example, if the physiological signalis an EMG signal indicative of the patient's muscle activity, a highlevel of muscle activity that falls outside of an acceptable range mayindicate that the PNFS is causing muscle spasms, which may beundesirable. The acceptable range of values may be determined, e.g.,using the technique described with reference to FIG. 10 or may bepreselected by a clinician and stored within IMD 14 and programmers 22,28.

In one example, processor 44 determines whether the amplitude of thephysiological signal is within an acceptable range of amplitude valuesby comparing the amplitude of the signal to an upper threshold value anda lower threshold value. In the case of an energy level in one or morefrequency bands, processor 44 determines whether the energy level iswithin an acceptable range by comparing the energy level of a frequencyband component of the signal to an upper threshold value and a lowerthreshold value. If the signal characteristic is a pattern in thephysiological signal, processor 44 determines whether the pattern iswithin an acceptable range by comparing the physiological signalwaveform to one or more templates.

If the signal characteristic is within an acceptable range (136),processor 44 continues delivering PNFS therapy according to the modifiedtherapy program until patient input is received. In this way, thepatient's input modifying a therapy program is regulated based on thephysiological effects of the PNFS on patient 12. In some cases,processor 44 may also continue monitoring the physiological signal (102)and may control the delivery of PNFS based on the signal, as describedwith respect to FIGS. 5-9.

If the signal characteristic is not within an acceptable range (136),processor 44 modifies the modified therapy program (138) in order togenerate or select a therapy program that maintains the physiologicalsignal characteristic within an acceptable range. For example, processor44 may modify the therapy program using any of the techniques describedabove with respect to FIG. 7, e.g., selecting another stored therapyprogram or modifying the therapy program using a genetic algorithm or atree-based structure. Alternatively, processor 44 may revert to thepreviously-implemented therapy program. Additionally, processor 44 mayprovide a notification to the patient regarding ineffectiveness of themodified therapy program, e.g., via patient programmer 28.

While the techniques described above with respect to FIGS. 5-11 discusscontrolling therapy system 10 based on a detected physiological effectof the PNFS therapy on patient 12, in other examples, therapy system 10may be controlled based on the detection of a pain state of patient 12.For example, as described below with reference to FIGS. 13 and 14, PNFSmay be delivered to patient 12 upon determining a pain state. A painstate refers to a patient state in which the delivery of PNFS to patient12 may provide relief of pain symptoms felt by patient 12. Acharacteristic of a physiological signal may be used to characterize apain state of patient 12.

FIG. 12 is a flow diagram illustrating a technique for associating apatient pain state with a characteristic of a physiological signal.Although the technique shown in FIG. 12 is described as being performedby processor 80 (FIG. 4) of patient programmer 28, in other examples,processor 60 of clinician programmer 22, processor 44 of IMD 14, or aprocessor of another computing device may associate patient pain stateswith one or more signal characteristics in accordance with the techniqueshown in FIG. 12. The technique shown in FIG. 12 may be performed byprocessor 80 during a learning period, which may be one day to multipledays.

Processor 80 of patient programmer 28 may receive a signal from sensingmodule 20 indicating activity of a physiological parameter of patient12, such as the patient's muscle activity or skin conductance (102).When patient 12 feels pain, patient 12 may provide input, e.g., viadisplay 30 or keypad 32 of user interface 84 (FIG. 4). Patient 12 mayindicate a pain state using any suitable technique. In one example,patient 12 merely indicates the occurrence of a pain state. For example,user interface 84 of patient programmer 28 may include a buttondedicated to recording the time and date of the pain state, and patient12 may depress the dedicated button. Alternatively, a multifunctionbutton may be used in combination with a particular user interfacedisplay to indicate the occurrence of a pain state. In other examples,patient 12 may indicate a type of pain state in addition to indicatingthe occurrence of a pain state, such as information regarding theseverity of the pain state or the location of the pain. For example,patient 12 may select a pain state from a predefined list of pain states(e.g., a list including moderate pain and severe pain), manually input apain state, select a numerical rating of the severity of the pain state(e.g., a numerical range of 1 through 10, where 10 indicates patient 12experienced a severe pain state). User interface 84 may present a visualscale, such as the Wong-Baker Faces Pain Rating Scale, and patient 12may select the relevant pain rating from the visual scale. Othertechniques for receiving input regarding a pain state of patient 12 arecontemplated.

Upon receiving patient input indicating a pain state (140), processor 80automatically determines a characteristic of a physiological signal(142). For example, processor 80 may use the technique described withrespect to FIG. 10 to determine the characteristic of the physiologicalsignal at the time the patient input was received or within a certaintime range including the time at which the patient input was received.Processor 80 associates the physiological signal characteristic with thepain state (144), and stores the information in control informationportion 92 of memory 82 (FIG. 4). The control information 92 may becommunicated to other devices, such as clinician programmer 22 (FIG. 3),IMD 14 (or IMD 56), or another computing device.

In some cases, upon request by a user, processor 80 may present a list,table or other data format illustrating the pain state (and any relevantpain ratings) and associated physiological signal characteristic viadisplay 30 of patient programmer 28. For example, if the physiologicalsignal characteristic includes a peak or average value of the waveformamplitude of the physiological signal within a certain time range of thepatient input, processor 80 may present a list of a plurality of painstates and associated physiological signal amplitude values. Thephysiological signal characteristics in the list may then be used as athreshold amplitude value for detecting a pain state. As anotherexample, if the physiological signal characteristic includes a trend inthe physiological signal waveform within a certain time range of thepatient input, processor 80 may present a list of pain states andprovide links to a visual representation of the waveform trend. Thewaveform trend may be used as a template for detecting a pain statebased on a physiological signal.

In some cases, the physiological signal characteristic may not provide adirect link to the existence or level of the patient's pain state, andmay instead be a surrogate marker that is suggestive of the patient painstate, rather than of pain or another pain-related symptom. Thus, theassociation between pain states and physiological signal characteristicsmay be somewhat inaccurate and imprecise. Furthermore, the patient inputregarding the pain state may be inaccurate or inconsistent. Accordingly,it may be desirable for the clinician or processor 80 to confirm that apain state is associated with a particular physiological signalcharacteristic prior to storing the physiological signal characteristicas control information 92. In some examples, processor 80 or theclinician may record the patient's pain state only after the same orsimilar physiological signal characteristic is associated with the painstate more than one time. If the physiological signal characteristic isan amplitude value, for example, a similar physiological signalcharacteristic may be within a particular range, such as about 5% toabout 20% of the amplitude value, although other ranges arecontemplated.

In some examples, after associating physiological signal characteristicswith pain states for one or more patients, a clinician or processor 80may generate a pain state probability for each physiological signalcharacteristic. Thus, rather than directly associating a patient painstate with a physiological signal characteristic, processor 80 mayassign a probability of the existence or severity of a pain state withthe physiological signal characteristic. For example, for a particularphysiological signal characteristic, processor 80 may determine that 85%of the time, patient 12 indicated a severe pain state. Programmer 80 maygenerate a library of physiological signal characteristics andassociated pain states or pain state probabilities. The library may bespecific to patient 12 (i.e., generated based on information frompatient 12) or may be more general, e.g., based on information from morethan one patient.

In some examples, the pain state information may be used to controltherapy delivery by IMD 14. FIGS. 13 and 14 are flow diagramsillustrating example techniques for controlling therapy delivery basedon a detected pain state. If patient 12 suffers from episodic pain,delivering therapy to patient 12 upon detection of a pain state may bean efficient and effective technique for detecting an episode of pain ofpatient 12 and providing on-demand therapy to patient 12. In the case ofboth chronic and episodic pain conditions, relief of pain may bemaintained for some time after delivery of efficacious PNFS is stopped,thus, although PNFS is not actively delivered to patient 12, patient 12may experience pain relief. Accordingly, delivering therapy to patient12 upon detection of a pain state may be an efficient technique formanaging chronic pain of patient 12. While processor 44 of IMD 14 isprimarily referred to in the description of FIGS. 13 and 14, in otherexamples, processor 60 of clinician programmer 22, processor 80 ofpatient programmer 28 or a processor of another device may control PNFStherapy delivery in accordance with the techniques shown in FIGS. 13 and14.

In the technique shown in FIG. 13, processor 44 monitors a physiologicalparameter of patient 12 to detect a patient pain state. In particular,processor 44 receives a physiological signal from sensing module 20(FIG. 1) (102) and determines whether a characteristic of thephysiological signal indicates patient 12 is in a pain state (148). Forexample, processor 44 may compare the amplitude value of the receivedphysiological signal to a threshold value, which may be determined,e.g., using the technique described above with respect to FIG. 12. Inother examples, processor 44 may determine whether the characteristic ofthe physiological signal indicates patient 12 is in a pain state (148)using the template matching and frequency band component analysistechniques similar to those described above with respect to FIGS. 8-9.

If processor 44 detects a pain state (148), processor 44 controlstherapy module 42 to initiate therapy delivery or modify a therapyprogram (150). In some examples, processor 44 selects a therapy programbased on the detected pain state. For example, different physiologicalsignal characteristics (e.g., amplitude values or waveform patterns orother morphologies) may be associated with different therapy programsthat have been determined by the clinician or processor 44 to provideefficacious therapy to manage the particular pain state of the patient.The clinician or processor 44 may associate the different therapyprograms with pain states during a programming session prior toimplantation of IMD 14 or after implantation of IMD 14 within patient12. The pain states, as characterized by a physiological signalcharacteristic or a range of values of the physiological signal, may beassociated with one or more therapy programs in memory 46 of IMD 14,memory 62 of clinician programmer 22 (FIG. 3), memory 82 of patientprogrammer 28 (FIG. 4) or a memory of another device. In some examples,upon detecting a pain state (148), processor 44 may determine which oneor more therapy programs are associated with the pain state and selectat least one of the therapy programs to deliver therapy to patient 12.

On the other hand, if processor 44 does not detect a pain state (148),processor 44 continues monitoring the physiological signal until a painstate is detected. In other examples, processor 44 determines aprobability of a pain state based on the characteristic of the receivedphysiological signal. If the probability of the pain state associatedwith the physiological signal characteristic exceeds a threshold level,such as greater than 50% to about 90%, processor 44 controls therapymodule 42 to initiate therapy delivery.

The technique shown in FIG. 13 may be implemented to provide closed-loopPNFS therapy to patient 12 as needed, e.g., upon the detection of a painstate. The on-demand therapy may help conserve power source 48 of IMD 14(FIG. 2A), and helps reduce patient adaptation to the therapy delivery,as discussed above.

As shown in FIG. 14, a patient state that is determined based on acharacteristic of a monitored physiological parameter may also be usedto deactivate and activate delivery of PNFS to patient 12. In accordancewith the technique shown in FIG. 14, processor 44 of IMD 14 deliversPNFS therapy to patient 12 according to a therapy program (96).Processor 44 controls IMD 14 to deliver the PNFS therapy to patient 12for a predetermined stimulation period, such as about 1 second to about1 hour. In some examples, the stimulation period may be set by aclinician. Other stimulation periods are contemplated, and may dependupon the type of pain experienced by patient 12.

After the stimulation period, therapy delivery may be deactivated (152),as shown in FIG. 14, or the intensity of the therapy delivery may bedecreased. Following the stimulation period, processor 44 may receive aphysiological signal from sensing device (102) and determine whether acharacteristic of the physiological signal indicates the presence of apain state (148). If the pain state is detected (148), processor 44controls therapy module 42 to resume delivering PNFS to region 18 withinpatient 12. If the pain state is not detected (148), processor 44continues monitoring the physiological signal without resuming thedelivery of PNFS to patient 12 (102). In this way, processor 44 maydeliver PNFS to patient 12 while patient 12 is in a pain state and maydeactivate or decrease the intensity of stimulation while patient 12 isnot in a pain state.

FIGS. 15A and 15B are flow diagrams illustrating an example techniquefor modifying a therapy program using control information that is basedon physiological signals indicative of a patient pain state. The controlinformation may be obtained and associated with a patient pain state ora particular physiological response, e.g., using the technique shown inFIG. 12 and may be stored within IMD 14, clinician programmer 22 orpatient programmer 28. While processor 44 of IMD 14 is primarilyreferred to in the description of FIGS. 15A and 15B, in other examples,processor 60 of clinician programmer 22, processor 80 of patientprogrammer 28 or a processor of another device may perform any part ofthe technique shown in FIGS. 15A-15B.

Processor 44 controls therapy module 42 to deliver PNFS to region 18 ofpatient 12 according to a first therapy program (96). Processor 44receives a physiological signal from sensing module 20 (102) anddetermines whether a characteristic of the physiological signal iswithin an acceptable range (136). As previously described, theacceptable range may indicate the range of values that reflect anacceptable physiologic response (e.g., a response that indicates patient12 is not in pain). In other examples, processor 44 may determinewhether a characteristic of the physiological signal from sensing module20 substantially matches a control signal, as described with respect toFIGS. 16 and 17. If the physiological signal is within the acceptablerange of values (136), processor 44 continues delivering PNFS therapyaccording to the first therapy program (96). If processor 44 determinesthat the physiological signal is not within an acceptable range (136),processor 44 determines that modification to the first therapy programis desirable because therapy delivery according to the first therapyprogram is not efficacious or not sufficiently efficacious. For example,patient 12 may have adapted to the first therapy program over time.

In some cases, processor 44 modifies the first therapy program toincrease the intensity of stimulation (154). The intensity ofstimulation may be increased by, for example, increasing at least one ofthe current or voltage amplitude of the first therapy program, thefrequency of the first therapy program, and, if the first therapyprogram defines electrical stimulation pulses, the pulse width of thefirst therapy program. In addition or instead of modifying the values ofthe amplitude, frequency or pulse width, processor 44 may modify theelectrode configuration that is used to deliver the PNFS, such as byincreasing the number of electrodes that are activated in order to yielda larger area of stimulation effect.

Increasing the intensity of stimulation may increase the total energyrequired by therapy module 42 (FIG. 2A) to generate and deliver thestimulation signals to region 18 (FIG. 1). In some examples, increasingthe intensity of stimulation may increase the total volume of thestimulation field generated by delivering the stimulation via electrodes40 (FIG. 2A). Increasing the total volume of the stimulation field mayincrease the activation field, which may represent the volume of neuraltissue that is activated by the stimulation signals.

After modifying the first therapy program to define a second therapyprogram including at least one therapy parameter value that differs fromthe first therapy program (154), processor 44 controls therapy module 42to deliver PNFS to region 18 according to the second therapy program(156). Processor 44 receives a physiological signal from sensing module20 (102) and determines whether a characteristic of the physiologicalsignal is within an acceptable range (136). If the physiological signalis not within the acceptable range (136), processor 44 may furtherincrease the intensity of stimulation (154) until the signal is withinthe acceptable range. If the physiological signal is within theacceptable range (136), processor 44 modifies the second therapy programto decrease the intensity of stimulation (158) and generate a thirdtherapy program. Decreasing the intensity may be useful for, forexample, determining whether the intensity may be decreased withoutdecreasing the physiological effect, as indicated by the physiologicalsignal from sensing module 22. Decreasing the intensity of stimulationmay help decrease the energy consumption by IMD 14.

The intensity of stimulation may be decreased (158) by modifying thesame or a different therapy parameter value as the stimulation parametermodified in order to increase the intensity of stimulation (154). Inaddition, the intensity of stimulation may be decreased using adifferent rate than the rate used to increase the intensity (154). Thatis, in some examples, processor 44 may increase the intensity ofstimulation (154) by increasing the value of a stimulation parameter bya first percentage or value, and processor 44 may decrease the intensityof stimulation (158) by decreasing the value of the same stimulationparameter by a second percentage or value that is lower than the firstpercentage or value.

Processor 44 s monitor the physiological effect of the third therapyprogram on patient 12 by delivering therapy to patient 12 according tothe third therapy program (160) and determining whether thephysiological signal characteristic is within an acceptable range (136).If the signal characteristic is still within the acceptable range,processor 44 may further decrease the intensity of stimulation (158)until the signal characteristic is outside the acceptable range (136).

After the intensity of stimulation is decreased to a point where thesignal characteristic is not within the acceptable range (136),processor 44 may modify the third therapy program to increase theintensity stimulation (162), thereby generating a fourth therapyprogram. In this iteration of increasing the intensity of stimulation,processor 44 may increase the intensity of stimulation by a smallerfactor (e.g., a percentage or incremental parameter value) than theprior modification to increase the stimulation intensity (154).

Processor 44 monitors the physiological effect of the fourth therapyprogram on patient 12 by delivering therapy to patient 12 according tothe fourth therapy program (164) and determining whether thephysiological signal characteristic is within an acceptable range (136).If the signal is not within an acceptable range (136), processor 44continues to increase the intensity of stimulation (162) until thesignal characteristic is within the acceptable range. If the signal iswithin an acceptable range, processor 44 stores the fourth therapyprogram within memory 46 (within therapy programs 52 section). In somecases, processor 44 may notify another device, such as clinicianprogrammer 22 or patient programmer 28, that the first therapy programwas modified, and may transmit information indicative of the therapyparameter values of the fourth therapy program to the other device. Inother examples, processor 44 may modify the fourth therapy program todecrease the intensity stimulation. In this iteration of decreasing theintensity of stimulation, processor 44 may decrease the intensity ofstimulation by a smaller factor (e.g., a percentage or incrementalparameter value) than the prior modification to decrease the stimulationintensity (158).

The technique shown in FIGS. 15A-15B may be used to determine amodification to a therapy program that increases the stimulationintensity and minimizes power usage in order to help conserve powersource 48 of IMD 14 (FIG. 2A). By increasing and decreasing theintensity of stimulation by iteratively smaller percentages or parametervalues (i.e., in each subsequent therapy program modification step),processor 44 may perform a binary-search type technique to determine atleast one therapy parameter value that maintains the physiologicaleffects of stimulation on patient 12 within a particular range, whileminimizing the energy required by IMD 14 to generate and deliver theefficacious stimulation therapy to patient 12.

Processor 44 may make any suitable number of iterations to decrease andincrease the intensity of stimulation. For example, in other examples,after the signal characteristic is within the acceptable range (136)following therapy delivery according to the third therapy program (160),processor 44 may store the third therapy program within memory 46(within therapy programs 52 section) rather than modifying the thirdtherapy program to increase the intensity of stimulation. As anotherexample, in other examples, after the signal characteristic is withinthe acceptable range (136) following therapy delivery according to thefourth therapy program (162), processor 44 may modify the fourth therapyprogram to decrease the intensity of stimulation.

Rather than controlling therapy module 42 of IMD 14 based on a storedphysiological characteristic (e.g., determined using the technique shownin FIG. 10), in other examples, processor 44 may control therapy module42 based on a received control physiological signal. The controlphysiological signal may be generated by a sensing module within IMD 14,by sensing module 20 (FIG. 1) or a separate sensing module. FIG. 16 is aconceptual diagram of therapy system 170 that includes sensing module172 that is separate from IMD 14 and sensing module 20. Therapy system170 is substantially similar to therapy system 10 of FIG. 1 and mayinclude IMD 14 coupled to lead 16 to deliver PNFS to region 18 of thepatient's body in which patient 12 perceives pain. Although not shown inFIG. 16, therapy system 170 may include clinician programmer 22 and/orpatient programmer 28, which may each be configured to communicate withsensing module 172.

Sensing module 172 may generate a control physiological signal thatindicates an activity of a physiological parameter of patient 12 at a“normal” level, e.g., generally unaffected by the patient's pain or thedelivery of PNFS. For example, if patient 12 experiences back spasmswithin region 18, sensing module 172 may be positioned to generate acontrol signal that reflects the physiological parameter activity withinan area of the patient's body that does not experience back spasms(e.g., another region within the back, which may reflect a baseline(normal) level of muscle activity). The control signal may indicate, forexample, muscle activity (e.g., EMG), skin temperature, blood flow, andthe like. Accordingly, in some examples, sensing module 172 may generatea control physiological signal that indicates activity of aphysiological parameter of patient 12 outside of the region 18 to whichIMD 14 delivers PNFS. For example, sensing module 172 may be implantedwithin patient 12 outside of region 18 (e.g., about 2 centimeters (cm)to 20 cm or greater from region) or may be external to patient 12outside of region 18, which includes the region of the patient'sepidermis that substantially corresponds to region 18. The signal fromsensing module 172 may be used to determine a physiological signalcharacteristic that does not result from the delivery of PNFS.

Sensing module 172 may transmit the control physiological signal to IMD14. The control signal may be sent substantially in real time, e.g.,indicating the current activity of the physiological parameter, such aswithin the previous 1 ms to about 1 second, although other time rangesor contemplated. In other examples, sensing module 172 may periodicallytransmit a control signal to IMD 14 that does not indicate the mostrecent activity of the physiological parameter, but may still generallyindicate a baseline state for the physiological signal generated bysensing module 20, which indicates the physiological effects of thePNFS.

In examples in which IMD 14 includes a sensing module that generates thecontrol physiological signal, IMD 14 may sense the physiologicalparameter outside of region 18 with electrodes that are coupled to lead16, which may include the same electrode array 40 as the array used todeliver PNFS. Depending on the relative size of region 18 compared tothe electrode array 40, electrode array 40 may include electrodes thatare both within region 18 to deliver PNFS to region and outside ofregion 18 to sense a physiological parameter. In examples in whichsensing module 20 (FIG. 1) is used to generate the control physiologicalsignal, sensing module 20 may also include electrodes that are withinregion 18 and outside of region 18. For example, one subset ofelectrodes of sensing module 20 may be used to detect the physiologicalsignal that indicates the physiological effects of PNFS and anothersubset of electrodes may be used to detect a control signal. The firstand second subsets of electrodes may be spaced from each other such thatsensing module 20 is capable of sensing the physiological parameter ofpatient 12 in different areas of the patient's body to distinguishbetween the physiological effects of the PNFS and the normalphysiological parameter levels (e.g., generally not reflecting thephysiological effects of the PNFS).

FIG. 17 is a flow diagram illustrating an example technique forcontrolling an implantable medical device based on a sensedphysiological parameter of the patient. While processor 44 of IMD 14 isprimarily referred to in the description of FIG. 17, in other examples,processor 60 of clinician programmer 22, processor 80 of patientprogrammer, or a processor of another device may control therapy module42 based on a control physiological signal generated by sensing module172.

Therapy module 42 of IMD 14 delivers PNFS to patient 12 according to atherapy program (96). As previously described, processor 44 of IMD 14may control therapy module 42 to deliver the PNFS. Processor 44 receivesa first physiological signal from sensing module 20, which indicates aphysiological effect of the PNFS or physiological parameter activitythat indicates the patient's pain (176). Processor 44 also receives asecond, control physiological signal from sensing module 172 (178),which indicates the physiological parameter activity of the patient thatis generally unaffected by the delivery of PNFS. For example, the secondphysiological signal may be generated within an area outside of region18 (FIG. 1) of the patient's body in which PNFS is delivered. Manyphysiological effects from PNFS may be relatively local in nature (e.g.,skin temperature, sweating, EMG, and the like), and, accordingly, thesecond physiological signal characteristic may be distanced from region18 (FIG. 1) a relatively small distance (e.g., about 2 cm to about 20 cmor greater).

Processor 44 compares the first physiological signal to the secondphysiological signal (180). In the example shown in FIG. 17, processor44 may determine a first characteristic of the first physiologicalsignal, such as a peak, average or median amplitude within a sample timewindow, a frequency characteristic (e.g., a power level within aselected frequency band or a ratio of powers), a pattern in the firstphysiological signal waveform over time, and so forth. Processor 44 mayalso determine a second characteristic of the second physiologicalsignal, where the type of second characteristic is similar to the firstcharacteristic (e.g., both may be amplitude values or patterns of thewaveforms). Processor 44 may then compare the first and secondcharacteristics (180).

If the first and second signal characteristics substantially match(182), processor 44 determines that the PNFS has been effective, andprocessor 44 controls therapy module 42 to deactivate the delivery ofPNFS to region 18 (108). Alternatively, processor 44 may merely decreasethe intensity of the PNFS delivered to region. If the first and secondsignal characteristics do not substantially match (182), processor 44may determine that the PNFS has not been effective, and processor maycontrol therapy module 42 of IMD 14 to resume or continue deliveringPNFS to the patient according to the therapy program (110).

In other examples, processor 44 may modify the therapy program if thefirst characteristic of the first physiological signal from sensingmodule 22 does not substantially match the corresponding characteristicof the second, control signal from sensing module 172. For example,similar to the technique shown in FIG. 7, processor 44 may determineefficacy indications based on the comparison between the firstphysiological signal from sensing module 22 and the second, controlsignal from sensing module 172. If the number of efficacy indicationsexceeds a threshold, processor 44 may determine that the current therapyprogram is ineffective and may modify the current therapy program, suchas by selecting a different therapy program or modifying one or morestimulation parameter values of the current therapy program.

Various examples have been described in this disclosure. These and otherexamples are within the scope of the following claims. For example,while PNFS is primarily described herein, the techniques for controllingtherapy delivery described herein may also be applicable to other typesof therapy, such as peripheral nerve stimulation (PNS). In addition,therapy system 10 may deliver PNFS to patient 12 in combination with oneor more other therapies, as described in U.S. patent application Ser.No. 11/450,133 to Rooney et al., which was previously incorporated byreference. Examples of other therapies include spinal cord stimulationor delivery of a therapeutic agent, anti-inflammatory agents such assteroids, NSAIDS, TNF-alpha inhibitors (soluble receptors, antibodies,etc.), local anesthetics, and NMDA antagonists (ketamine, etc.).

In addition, in other examples, PNFS may be delivered by an IMDincluding electrodes on one or more surfaces of the IMD housing, asdescribed in commonly-assigned U.S. patent application Ser. No.11/450,127 to Rooney et al., entitled, “IMPLANTABLE MEDICAL DEVICE WITHELECTRODES ON MULTIPLE HOUSINGS SURFACES,” which was filed on Jun. 9,2006 and is incorporated herein by reference in its entirety. Examplesof therapeutic agents for relieving pain are also described incommonly-assigned U.S. patent application Ser. No. 11/374,852 to Heruthet al., entitled, “REGIONAL THERAPIES FOR TREATMENT OF PAIN,” which wasfiled on Mar. 14, 2006 and is incorporated herein by reference in itsentirety.

The techniques described in this disclosure, including those attributedto IMD 14, clinician programmer 22, patient programmer 28, or variousconstituent components, may be implemented, at least in part, inhardware, software, firmware or any combination thereof. For example,various aspects of the techniques may be implemented within one or moreprocessors, including one or more microprocessors, DSPs, ASICs, FPGAs,or any other equivalent integrated or discrete logic circuitry, as wellas any combinations of such components, embodied in programmers, such asphysician or patient programmers, stimulators, image processing devicesor other devices. The term “processor” or “processing circuitry” maygenerally refer to any of the foregoing logic circuitry, alone or incombination with other logic circuitry, or any other equivalentcircuitry.

Such hardware, software, firmware may be implemented within the samedevice or within separate devices to support the various operations andfunctions described in this disclosure. While the techniques describedherein are primarily described as being performed by processor 44 of IMD14, processor 60 of clinician programmer 22, and/or processor 80 ofclinician programmer 28, any one or more parts of the techniquesdescribed herein may be implemented by a processor of one of IMD 14,clinician programmer 22, patient programmer 28, or another computingdevice, alone or in combination with each other.

In addition, any of the described units, modules or components may beimplemented together or separately as discrete but interoperable logicdevices. Depiction of different features as modules or units is intendedto highlight different functional aspects and does not necessarily implythat such modules or units must be realized by separate hardware orsoftware components. Rather, functionality associated with one or moremodules or units may be performed by separate hardware or softwarecomponents, or integrated within common or separate hardware or softwarecomponents.

When implemented in software, the functionality ascribed to the systems,devices and techniques described in this disclosure may be embodied asinstructions on a computer-readable medium such as RAM, ROM, NVRAM,EEPROM, FLASH memory, magnetic data storage media, optical data storagemedia, or the like. The instructions may be executed to support one ormore aspects of the functionality described in this disclosure.

Various examples of the disclosure have been described. These and otherexamples are within the scope of the following example statements.

1. A method comprising: delivering peripheral nerve field stimulation toa region of a body of a patient in which the patient experiences painvia at least one electrode implanted in the region; receiving a signalindicative of a physiological parameter of the patient, wherein thesignal indicates a response of the patient to the peripheral nerve fieldstimulation; and controlling the delivery of the peripheral nerve fieldstimulation based on the signal.
 2. The method of claim 1, whereindelivering peripheral nerve field stimulation comprises deliveringelectrical stimulation therapy to activate sensory afferent nerve fibersof the patient.
 3. The method of claim 1, wherein the response comprisesan efferent response.
 4. The method of claim 1, wherein receiving thesignal comprises receiving the signal that is indicative of at least oneof a heart rate, respiratory rate, electrodermal activity, muscleactivity, blood flow rate, sweat gland activity, pilomotor reflex orthermal activity of the patient.
 5. The method of claim 1, whereindelivering peripheral nerve field stimulation comprises deliveringperipheral nerve field stimulation according to a therapy programdefining values for a plurality of therapy parameters, and controllingthe delivery of peripheral nerve field stimulation comprisesautomatically modifying a value of at least one of the therapyparameters.
 6. The method of claim 1, wherein delivering peripheralnerve field stimulation comprises delivering peripheral nerve fieldstimulation according to a first therapy program, and controlling thedelivery of peripheral nerve field stimulation comprises selecting asecond therapy program and initiating the delivery of peripheral nervefield stimulation according to the second therapy program.
 7. The methodof claim 1, wherein controlling the delivery of the peripheral nervefield stimulation comprises deactivating the delivery of the peripheralnerve field stimulation.
 8. The method of claim 1, wherein controllingthe delivery of the peripheral nerve field stimulation comprisesinitiating the delivery of the peripheral nerve field stimulation. 9.The method of claim 1, further comprising comparing an amplitude of thesignal to a threshold value, wherein controlling the delivery of theperipheral nerve field stimulation comprises controlling the delivery ofthe peripheral nerve field stimulation based on the comparison betweenthe amplitude of the signal and the threshold value.
 10. The method ofclaim 9, wherein the threshold value is determined based on patientinput that indicates an acceptable or unacceptable physiological effectof the delivery of peripheral nerve field stimulation.
 11. The method ofclaim 1, further comprising comparing a pattern of a waveform of thesignal to a template, wherein controlling the delivery of the peripheralnerve field stimulation comprises controlling the delivery of theperipheral nerve field stimulation based on the comparison between thepattern of the waveform of the signal and the template.
 12. The methodof claim 1, further comprising determining a first frequency componentof a waveform of the signal and comparing the first frequency componentto a second frequency component of a waveform template, whereincontrolling the delivery of the peripheral nerve field stimulationcomprises controlling the delivery of the peripheral nerve fieldstimulation based on the comparison between the first and secondfrequency components.
 13. The method of claim 1, wherein the signalcomprises a first signal, the method further comprising: receiving asecond signal indicative of the physiological parameter of the patient;and comparing a first characteristic of the first signal to a secondcharacteristic of the second signal, wherein controlling the delivery ofthe peripheral nerve field stimulation comprises controlling thedelivery of the peripheral nerve field stimulation based on thecomparison of the first and second characteristics.
 14. The method ofclaim 13, wherein second signal changes as a function of thephysiological parameter of the patient outside of the region of the bodyin which the patient experiences pain.
 15. The method of claim 13,further comprising determining the first characteristic and the secondcharacteristic, the first and second characteristics comprising at leastone of an amplitude value, an energy level within a frequency band ofthe respective first or second signals or a pattern in a waveform of therespective first or second signals.
 16. The method of claim 1, whereinthe signal comprises a first signal, the method further comprisingreceiving a second signal indicative of a second physiological parameterof the patient, wherein the second signal indicates the response of thepatient to the peripheral nerve field stimulation, wherein controllingthe delivery of the peripheral nerve field stimulation comprisescontrolling the delivery of the peripheral nerve field stimulation basedon the first and second signals.
 17. The method of claim 16, whereincontrolling the delivery of the peripheral nerve field stimulation basedon the first and second signals comprises controlling the delivery ofthe peripheral nerve field stimulation to maintain a firstcharacteristic of the first signal within a first range of values andmaintain a second characteristic of the second signal within a secondrange of values.
 18. A method comprising: delivering peripheral nervefield stimulation to a region of a body of a patient in which thepatient experiences pain via at least one electrode implanted in theregion; detecting an efferent response of the patient to the delivery ofperipheral nerve field stimulation; and controlling the delivery ofelectrical stimulation therapy based on the detected efferent response.19. The method of claim 18, wherein detecting the efferent responsecomprises detecting at least one of a heart rate, respiratory rate,electrodermal activity, muscle activity, blood flow rate, sweat glandactivity, pilomotor reflex or thermal activity of the patient.
 20. Asystem comprising: a sensing module that generates a signal indicativeof a physiological parameter of a patient; a medical device thatdelivers peripheral nerve field stimulation to a region of a body of thepatient in which the patient experiences pain via at least one electrodeimplanted in the region; and a processor that receives the signal fromthe sensing module and controls the delivery of the peripheral nervefield stimulation by the medical device based on the signal, wherein thesignal indicates a response of the patient to the peripheral nerve fieldstimulation.
 21. The system of claim 20, wherein the physiologicalparameter comprises at least one of a heart rate, respiratory rate,electrodermal activity, muscle activity, blood flow rate, sweat glandactivity, pilomotor reflex or thermal activity of the patient.
 22. Thesystem of claim 20, wherein the medical device includes the sensingmodule.
 23. The system of claim 20, wherein the sensing module isphysically separate from the medical device.
 24. The system of claim 20,wherein the signal indicates an efferent response of the patient to theperipheral nerve field stimulation.
 25. The system of claim 20, whereinthe medical device delivers peripheral nerve field stimulation accordingto a therapy program, and the processor controls the delivery ofperipheral nerve field stimulation by automatically modifying thetherapy program.
 26. The system of claim 20, wherein the processorcontrols the delivery of peripheral nerve field stimulation by at leastone of deactivating or initiating delivery of peripheral nerve fieldstimulation to the patient by the medical device.
 27. The system ofclaim 20, wherein the sensing module comprises a first sensing modulethat generates a first signal that indicates a response of the patientto the peripheral nerve field stimulation, the system further comprisinga second sensing module that generates a second signal indicative of thephysiological parameter of the patient, wherein the processor compares afirst characteristic of the first signal to a second characteristic ofthe second signal, and controls the delivery of the peripheral nervefield stimulation based on the comparison of the first and secondcharacteristics.
 28. The system of claim 27, wherein the second sensingmodule is positioned to generate the second signal indicative of anactivity of the physiological parameter of the patient outside of theregion of the body in which the patient experiences pain.
 29. The systemof claim 27, w herein the second signal does not indicate any responseof the patient to the peripheral nerve field stimulation.
 30. The systemof claim 27, wherein the processor determines the first characteristicand the second characteristic, the first and second characteristicscomprising at least one of an amplitude value, an energy level within afrequency band of the respective first or second signals or a pattern ina waveform of the respective first or second signals.
 31. The system ofclaim 20, wherein the signal comprises a first signal, wherein theprocessor receives a second signal indicative of a second physiologicalparameter of the patient, the second signal indicating the response ofthe patient to the peripheral nerve field stimulation, and wherein theprocessor controls the delivery of the peripheral nerve fieldstimulation based on the first and second signals.
 32. A systemcomprising: means for delivering peripheral nerve field stimulation to aregion of a body of a patient in which the patient experiences pain viaat least one electrode implanted in the region; means for receiving asignal indicative of a physiological parameter of the patient, whereinthe signal indicates a response of the patient to the peripheral nervefield stimulation; and means for controlling the delivery of theperipheral nerve field stimulation based on the physiological signal.33. The system of claim 32, further comprising means for generating thesignal, wherein the means for generating the signal generates the signalindicative of at least one of a heart rate, respiratory rate,electrodermal activity, muscle activity, blood flow rate, sweat glandactivity, pilomotor reflex or thermal activity of the patient.
 34. Thesystem of claim 32, further comprising: means for receiving a secondsignal indicative of the physiological parameter of the patient; andmeans for comparing a first characteristic of the first signal to asecond characteristic of the second signal, wherein controlling thedelivery of the peripheral nerve field stimulation comprises controllingthe delivery of the peripheral nerve field stimulation based on thecomparison of the first and second characteristics.
 35. A methodcomprising: receiving a signal indicative of a physiological parameterof a patient; determining a patient pain state based on the signal; andbased on the patient pain state, controlling the delivery of peripheralnerve field stimulation to a region of a body of the patient in whichthe patient experiences pain via at least one electrode implanted in theregion.
 36. The method of claim 35, wherein controlling the delivery ofthe peripheral nerve field stimulation comprises initiating the deliveryof the peripheral nerve field stimulation.
 37. The method of claim 35,further comprising, prior to determining the patient pain state,delivering peripheral nerve field stimulation to the region of the bodyof the patient in which the patient experiences pain via the at leastone electrode implanted in the region, wherein controlling the deliveryof the peripheral nerve field stimulation comprises deactivating thedelivery of the peripheral nerve field stimulation.
 38. The method ofclaim 35, further comprising, prior to determining the patient painstate, delivering peripheral nerve field stimulation to the region ofthe body of the patient in which the patient experiences pain via the atleast one electrode implanted in the region, wherein controlling thedelivery of the peripheral nerve field stimulation comprises continuingthe delivery of the peripheral nerve field stimulation.
 39. The methodof claim 35, wherein controlling the delivery of the peripheral nervefield stimulation comprises modifying a therapy program based on thepatient pain state.
 40. The method of claim 35, wherein controlling thedelivery of the peripheral nerve field stimulation comprises selecting atherapy program based on the patient pain state.
 41. The method of claim35, further comprising: receiving patient input indicating the patientpain state; and associating the patient pain state with a characteristicof the signal, wherein controlling the delivery of the peripheral nervefield stimulation comprises detecting the characteristic of the signal.42. The method of claim 35, wherein determining the patient pain statecomprises at least one of comparing a peak amplitude of the signal to athreshold amplitude, comparing an average amplitude of the signal to thethreshold amplitude, comparing a median amplitude of the signal to thethreshold amplitude, comparing a trend in a waveform of the signal overtime to a template, comparing a power level within one or more frequencybands of the signal to a threshold power level or comparing a ratio ofpower levels in two or more frequency bands of the signal to a thresholdpower level ratio
 43. The method of claim 35, wherein the physiologicalparameter comprises at least one of a heart rate, respiratory rate,electrodermal activity, muscle activity, blood flow rate, sweat glandactivity, pilomotor reflex or thermal activity of the patient.
 44. Asystem comprising: a sensing module that generates a signal indicativeof a physiological parameter of a patient; a medical device thatdelivers peripheral nerve field stimulation to a region of a body of thepatient in which the patient experiences pain via at least one electrodeimplanted in the region; and a processor that receives the signal fromthe sensing module, determines a patient pain state based on the signal,and controls the medical device to deliver the peripheral nerve fieldstimulation to the patient based on the determined pain state.
 45. Thesystem of claim 44, wherein the sensing module generates a signalindicative of at least one of a heart rate, respiratory rate,electrodermal activity, muscle activity, blood flow rate, sweat glandactivity, pilomotor reflex or thermal activity of the patient.
 46. Thesystem of claim 44, wherein the processor initiates the delivery of theperipheral nerve field stimulation based on the determined pain state.47. The system of claim 44, wherein the medical device deliversperipheral nerve field stimulation to the region of the body of thepatient during a stimulation period, wherein the processor determinesthe patient pain state after the stimulation period.
 48. The system ofclaim 44, wherein the processor deactivates the delivery of theperipheral nerve field stimulation based on the determined pain state.49. The system of claim 44, wherein the processor modifies a therapyprogram based on the patient pain state.
 50. The system of claim 44,further comprising a memory that stores a plurality of therapy programsand information associating at least two of the therapy programs withdifferent patient pain states, wherein the processor selects at leastone of the plurality of therapy programs stored in the memory based onthe patient pain state.
 51. The system of claim 44, wherein theprocessor receives patient input indicating the patient pain state andassociates the patient pain state with a characteristic of the signal.52. The system of claim 44, wherein the processor determines the patientpain state by at least one of comparing a peak amplitude of the signalto a threshold amplitude, comparing an average amplitude of the signalto the threshold amplitude, comparing a median amplitude of the signalto the threshold amplitude, comparing a trend in a waveform of thesignal over time to a template, comparing a power level within one ormore frequency bands of the signal to a threshold power level orcomparing a ratio of power levels in two or more frequency bands of thesignal to a threshold power level ratio.
 53. A system comprising: meansfor receiving a signal indicative of a physiological parameter of apatient; means for determining a patient pain state based on the signal;and means for controlling delivery of peripheral nerve field stimulationto a region of a body of the patient in which the patient experiencespain based on the patient pain state, wherein the peripheral nerve fieldstimulation is delivered via at least one electrode implanted in theregion.
 54. The system of claim 53, further comprising means forreceiving patient input indicating the patient pain state and means forassociating the patient pain state with a characteristic of the signal,wherein the means for controlling the delivery of peripheral nerve fieldstimulation comprises means for detecting the characteristic of thesignal.